Catheter sensing and irrigating

ABSTRACT

Ablation systems of the present disclosure facilitate the safe formation of wide and deep lesions. For example, ablation systems of the present disclosure can allow for the flow of irrigation fluid and blood through an expandable ablation electrode, resulting in efficient and effective cooling of the ablation electrode as the ablation electrode delivers energy at a treatment site of the patient. Additionally, or alternatively, ablation systems of the present disclosure can include a deformable ablation electrode and a plurality of sensors that, in cooperation, sense the deformation of the ablation electrode, to provide a robust indication of the extent and direction of contact between the ablation electrode and tissue at a treatment site.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Prov. App. No. 62/330,395, filed May 2, 2016, U.S. Prov. App. No.62/357,704, filed Jul. 1, 2016, U.S. Prov. App. No. 62/399,632, filedSep. 26, 2016, U.S. Prov. App. No. 62/399,625, filed Sep. 26, 2016, U.S.Prov. App. No. 62/420,610, filed Nov. 11, 2016, U.S. Prov. App. No.62/424,736, filed Nov. 21, 2016, U.S. Prov. App. No. 62/428,406, filedNov. 30, 2016, U.S. Prov. App. No. 62/434,073, filed Dec. 14, 2016, U.S.Prov. App. No. 62/468,339, filed Mar. 7, 2017, and U.S. Prov. App. No.62/468,873, filed Mar. 8, 2017, with the entire contents of each ofthese applications hereby incorporated herein by reference.

This application is also related to the following commonly-owned U.S.patent applications filed on even date herewith: Attorney Docket NumberAFRA-0009-P01, entitled “LESION FORMATION”; Attorney Docket NumberAFRA-00010-P01, entitled “PULSED RADIOFREQUENCY ABLATION”; AttorneyDocket Number AFRA-0011-P01, entitled “THERAPEUTIC CATHETER WITHIMAGING,” and Attorney Docket Number AFRA-0013-P01, entitled “CATHETERINSERTION.” Each of the foregoing applications is hereby incorporatedherein by reference in its entirety.

BACKGROUND

Abnormal rhythms generally referred to as arrhythmia can occur in theheart. Cardiac arrhythmias develop when abnormal conduction in themyocardial tissue modifies the typical heartbeat pattern. Radiofrequency (“RF”) catheter ablation can be used to form lesions thatinterrupt the mechanism of abnormal conduction to terminate certainarrhythmias.

SUMMARY

Ablation systems of the present disclosure facilitate the safe formationof wide and deep lesions. For example, ablation systems of the presentdisclosure can allow for the flow of irrigation fluid and blood throughan expandable ablation electrode, resulting in efficient and effectivecooling of the ablation electrode as the ablation electrode deliversenergy at a treatment site of the patient. Additionally, oralternatively, ablation systems of the present disclosure can include adeformable ablation electrode and a plurality of sensors that, incooperation, sense the deformation of the ablation electrode, to providea robust indication of the extent and direction of contact between theablation electrode and tissue at a treatment site.

According to one aspect, a catheter including a catheter shaft, anirrigation element, and an ablation electrode. The catheter shaft has aproximal end portion and a distal end portion, the catheter shaftdefining a lumen extending from the proximal end portion to the distalend portion. The irrigation element is coupled to the distal end portionof the catheter shaft, the irrigation element defining irrigation holesin fluid communication with the lumen. The ablation electrode is coupledto the catheter shaft, the ablation electrode having an inner portionand an outer portion opposite the inner portion, wherein the irrigationholes of the irrigation element are directed toward the inner portion ofthe ablation electrode.

In certain implementations, at least some of the irrigation holes canhave a maximum dimension and, in the absence of external force appliedto the ablation electrode, the ratio of the maximum dimension of eachirrigation hole to a respective perpendicular distance between theirrigation hole and the inner portion of the ablation electrode can begreater than about 0.02 and less than about 0.2.

In some implementations, the total area of the irrigation holes can begreater than about 0.05 mm2 and less than about 0.5 mm2.

In certain implementations, the ablation electrode can envelop theirrigation element. Additionally, or alternatively, a volume defined bythe inner portion of the ablation electrode in an expanded state can belarger than a volume defined by the irrigation element in an expandedstate. For example, in the absence of external force applied to theablation electrode, the ablation electrode can include a portioncontained between a first radius and a second radius, the first radiusand the second radius within 30 percent of one another. As an additionalor alternative example, in the absence of external force applied to theablation electrode, the ablation electrode can include a substantiallyspherical portion. In certain instances, the ablation electrode canalso, or instead, include a substantially conical proximal region.

In some implementations, the irrigation element can be expandable. Forexample, the irrigation element, in an expanded state, can include anellipsoidal portion.

In certain implementations, the ablation electrode can be expandable.

In some implementations, the irrigation holes can be spacedcircumferentially and axially along the irrigation element.

In certain implementations, at least a portion of the irrigation holescan be arranged to direct fluid in a distal direction with respect tothe ablation electrode, and at least a portion of the irrigation holescan be arranged to direct fluid in a proximal direction with respect tothe ablation electrode.

In some implementations, the irrigation element can include one of anon-compliant balloon or a semi-compliant balloon.

In certain implementations, the irrigation element can be a resilient,expandable structure.

In some implementations, the irrigation element can include a porousmembrane.

In certain implementations, the irrigation element can include anopen-cell foam.

In some implementations, at least one of the irrigation element or theablation electrode can be expandable to have a cross-sectional dimensionlarger than a cross-sectional diameter of the catheter shaft.

In certain implementations, the irrigation element can be electricallyisolated from the ablation electrode.

In some implementations, the irrigation element can be electricallyisolated from the ablation electrode over a predetermined frequencyrange.

In certain implementations, the catheter can further include a centerelectrode disposed along the irrigation element.

In some implementations, the irrigation element can be thermallyisolated from the ablation electrode.

In certain implementations, the catheter can further include athermocouple disposed along the irrigation element.

In some implementations, the catheter can further include a handlecoupled to the proximal end portion of the catheter shaft, the handleincluding an actuation portion configured to actuate deflection of thecatheter shaft.

In certain implementations, the catheter can further include a pluralityof sensors, and the ablation electrode can include a deformable portionand the plurality of sensors is supported on the deformable portion ofthe ablation electrode. For example, at least one of the sensors can bemovable into contact with the irrigation element when a threshold forceis exceeded along the deformable portion of the ablation electrode.Continuing with this example, none of the plurality of sensors are incontact with an irrigation element, in certain instances, when thedeformable portion of the ablation electrode is in an uncompressedstate.

According to another aspect, a method of ablation tissue in a humanpatient can include positioning an ablation electrode at a treatmentsite (the ablation electrode having an outer portion disposed towardtissue and an inner portion opposite the outer portion), directingenergy to some of the outer portion of the ablation electrode, andproviding a flow of irrigation fluid at the inner portion of theelectrode, the flow of irrigation fluid having a Reynolds number greaterthan about 2300 at the inner portion of the ablation electrode, in theabsence of external force applied to the ablation electrode.

In certain implementations, providing the flow of irrigation fluid caninclude pumping irrigation fluid through a plurality of irrigation holesdefined by an irrigation element enveloped by the ablation electrode,and the irrigation element and the ablation electrode can each becoupled to a distal end portion of a catheter shaft. For example,pumping irrigation fluid through the irrigation holes can includedirecting at least a portion of the irrigation fluid in a directiondistal to the irrigation element and at least a portion of theirrigation fluid in a direction proximal to the irrigation element.

In some implementations, the method can further include delivering theablation electrode and the irrigation element to a tissue treatmentsite. For example, the ablation electrode and the irrigation element caneach be coupled to a distal end portion of a catheter shaft, anddelivery of the ablation electrode and the irrigation element to thetissue treatment site can includes moving the ablation electrode and theirrigation element, each in a collapsed state, through an 8F introducersheath.

According to another aspect, a catheter can include a catheter shaft, anirrigation element, and an ablation electrode. The catheter shaft canhave a proximal end portion and a distal end portion, the catheter shaftdefining a lumen extending from the proximal end portion to the distalend portion. The irrigation element can be coupled to the distal endportion of the catheter shaft, the irrigation element in fluidcommunication with the lumen. The ablation electrode can be coupled tothe catheter shaft. The ablation electrode can have an inner portion andan outer portion opposite the inner portion. Additionally, oralternatively, the ablation electrode can include a deformable portion,the deformable portion resiliently flexible from a compressed state toan uncompressed state, the inner portion of the ablation electrode alongthe deformable portion is closer in the compressed state than in theuncompressed state to at least a portion of a surface of the irrigationelement.

In certain implementations, the ablation electrode can be movable fromthe uncompressed state to the compressed state by a compression forcegreater than about 5 grams.

In some implementations, the irrigation element can define a pluralityof irrigation holes in fluid communication with the lumen, with morethan one irrigation hole of the plurality of irrigation holes arrangedalong the irrigation element to direct fluid toward the inner portion ofthe ablation electrode along the deformable portion. For example, theirrigation element can include a porous membrane. Additionally, oralternatively, the irrigation element can include an open-cell foam.Further, or instead, in an expanded state, the irrigation element caninclude an ellipsoidal portion (e.g., a balloon). In certain instances,the irrigation holes can be spaced circumferentially and axially alongthe irrigation element. In some instances, at least a portion of theirrigation holes can be arranged to direct fluid in a distal directionwith respect to the ablation electrode, and at least a portion of theirrigation holes can be arranged to direct fluid in a proximal directionwith respect to the ablation electrode.

In certain implementations, the deformable portion of the ablationelectrode can be resiliently flexible in an axial direction relative tothe catheter shaft and in a radial direction relative to the cathetershaft. Additionally, or alternatively, in the uncompressed state, thedeformable portion of the ablation electrode can envelop the irrigationelement. In certain instances, the irrigation element can be expandablefrom a delivery state to an expanded state.

In some implementations, the ablation electrode can have a conductivesurface, the conductive surface having greater than about 50 percent andless than about 95 percent open area along both the inner portion andthe outer portion.

In certain implementations, the ablation electrode can be a mesh.

In some implementations, the ablation electrode is a braid.

In certain implementations, the ablation electrode is formed of nitinol.For example, the ablation electrode can be formed of coated nitinol. Thecoating can be, by way of example, gold tantalum, or a combinationthereof.

In some implementations, the ablation electrode can be at leastpartially radiopaque.

In certain implementations, the irrigation element can include a balloonformed of one or more of: thermoplastic polyurethane, silicone,poly(ethylene terephthalate), and polyether block amide.

In some implementations, the catheter can further include a plurality ofsensors supported on the deformable portion of the ablation electrode.For example, at least one of the sensors can be movable into contactwith the irrigation element when a threshold force on the deformableportion of the ablation electrode is exceeded. Additionally, oralternatively, when the deformable portion of the ablation electrode isin the uncompressed state none of the plurality of sensors supported onthe deformable portion of the ablation electrode are in contact with theirrigation element, in certain instances. The deformable portion of theablation electrode, in the uncompressed state, can include, as anexample, an ellipsoidal portion and the sensors of the plurality ofsensors can be spaced from one another in a circumferential directionalong an inner portion of the ellipsoidal portion of the ablationelectrode. For example, the sensors of the plurality of sensors can beuniformly spaced in the circumferential direction along the ellipsoidalportion of the inner portion of the ablation electrode. Further, orinstead, the plurality of sensors can include a first set of sensors anda second set of sensors, the first set of sensors can be disposed distalto the second set of sensors along the inner portion of the ablationelectrode. In certain instances, the sensors of the plurality of sensorscan be substantially uniformly distributed along the inner portion ofthe ablation electrode. Also, or instead, at least one of the sensorscan include a radiopaque portion. Additionally, or alternatively, thecatheter can include at least one radiopaque marker disposed on theablation electrode (e.g., supported on at least one of the sensors).

In certain implementations, the irrigation element and the deformableportion of the ablation electrode can be collapsible to a sizedeliverable through an 8F introducer sheath.

According to still another aspect, a catheter ablation system includes acatheter and a controller. The catheter can include a catheter shaft, anirrigation element, and an ablation electrode, and a plurality ofsensors. The catheter shaft can have a proximal end portion and a distalend portion, the catheter shaft defining a lumen extending from theproximal end portion to the distal end portion. The irrigation elementcan be coupled to the distal end portion of the catheter shaft, theirrigation element in fluid communication with the lumen. The ablationelectrode can be coupled to the catheter shaft, the ablation electrodehaving an inner portion and an outer portion opposite the inner portion.The ablation electrode can include a deformable portion, the deformableportion resiliently flexible from a compressed state to an uncompressedstate, the inner portion of the ablation electrode along the deformableportion being closer in the compressed state than in the uncompressedstate to at least a portion of a surface of the irrigation element. Theplurality of sensors can be supported on the deformable portion of theablation electrode. The controller can be configured to: i) receive ameasurement resulting from an electrical signal generated between atleast one of the sensors and another electrode; and ii) based at leastin part on the measurement, determining a state of the deformableportion of the ablation electrode.

In certain implementations, the determined state of the deformableportion of the ablation electrode can correspond to a shape of thedeformable portion of the ablation electrode.

In some implementations, the controller can be further configured tosend an indication of the determined shape of the deformable portion ofthe ablation electrode to a graphical user interface.

In certain implementations, the controller can be further configured tosend electrical energy between at least one of the sensors and theirrigation element, and the received measurement can be based on theelectrical energy between the at least one of the sensors and theirrigation element.

In some implementations, the catheter ablation system can furtherinclude a center electrode disposed about the irrigation element. Thecontroller can be further configured to send electrical energy betweenat least one of the sensors and the center electrode, and the receivedmeasurement can be based on the electrical energy between the at leastone of the sensors and the center electrode.

According to still another aspect, a method of determining shape of anablation catheter can include receiving a measurement resulting from anelectrical signal generated between at least one sensor (supported on adeformable portion of an ablation electrode) and another electrode,based at least in part on the measurement, determining whether thedeformable portion of an ablation electrode is in contact with anirrigation element enveloped by the deformable portion of the ablationelectrode, and sending, to a graphical user interface, an indication ofthe determined contact between the deformable portion of the ablationelectrode and the irrigation element.

In certain implementations, determining the shape of the deformableportion of the ablation catheter can include determining athree-dimensional shape of the deformable portion of the ablationcatheter.

According to still another aspect, a method of making an ablationcatheter includes coupling an irrigation element to a distal end portionof a catheter shaft such that the irrigation element is in fluidcommunication with a lumen defined by the catheter shaft, forming adeformable portion of an ablation electrode, positioning deformableportion of the ablation electrode relative to the irrigation elementsuch that an inner portion of the ablation electrode envelops theirrigation element, and coupling the deformable portion of the ablationelectrode to the catheter shaft relative to the irrigation element, theinner portion of the ablation electrode along the deformable portionmovable between a compressed state and an uncompressed state, the innerportion of the ablation electrode being closer in a compressed than inan uncompressed state to a least a portion of a surface of theirrigation element.

In certain implementations, forming the deformable portion of theablation electrode can include removing material from a tube of material(e.g., nitinol) and bending the tube of material into a substantiallyenclosed shape.

In some implementations, forming the deformable portion of the ablationelectrode can include removing material from a flat sheet of material(e.g., nitinol) and bending the flat sheet of material into athree-dimensional shape. For example, removing material from the flatsheet of material can include laser cutting the flat sheet of material.Additionally, or alternatively, removing material from the flat sheet ofmaterial includes chemically etching the flat sheet of material.

According to yet another aspect, a catheter can include a catheter shafthaving a proximal end portion and a distal end portion, and an ablationelectrode coupled to the distal end portion of the catheter shaft. Theablation electrode can include struts coupled to one another at jointsto define collectively a plurality of cells. Each cell of the pluralityof cells can be bounded and the coupled struts can be movable relativeto one another such that a maximum radial dimension of the ablationelectrode increases by at least a factor of two as the coupled strutsmove relative to one another to transition the ablation electrode from acompressed state, in the presence of external force, to an uncompressedstate, in the absence of external force.

In some implementations, the struts can be in electrical communicationwith one another to form a single electrical conductor.

In certain implementations, the struts can be movable relative to oneanother to self-expand the ablation electrode from the compressed stateto the uncompressed state.

In some implementations, the ablation electrode can include an innerportion and an outer portion, opposite the inner portion, and the innerportion is in fluid communication with the outer portion through theplurality of cells.

In certain implementations, in the uncompressed state, at least some ofthe struts can extend circumferentially with respect to an axis definedby the proximal end portion and the distal end portion of the cathetershaft.

In some implementations, the ablation electrode can have a maximum axialdimension that changes by less than about 33 percent as the coupledstruts move relative to one another to expand the ablation electrodefrom the uncompressed state to the compressed state upon a change in anexternal radial force applied to the ablation electrode.

In certain implementations, in the uncompressed state, the maximumradial dimension of the ablation electrode is at least about 20 percentgreater than an outer diameter of the distal end portion of the cathetershaft.

In some implementations, the ablation electrode can be bulbous in theuncompressed state.

In certain implementations, the catheter shaft can define a center axisextending from the proximal end portion to the distal end portion, andat least some of the cells of the plurality of cells can have arespective symmetry plane passing through the respective cell andcontaining the center axis of the catheter shaft. For example, each cellof the plurality of cells can be symmetric about its respective symmetryplane in the compressed state and in the uncompressed state of theablation electrode.

In some implementations, the catheter shaft can define a center axisextending from the proximal end portion to the distal end portion, andat least some of the cells of the plurality of cells can have arespective symmetry plane passing through a distal end of the cell, aproximal end of the cell, and the center axis.

In certain implementations, the ablation electrode can include a distalregion and a proximal region, the proximal region coupled to the distalend portion of the catheter, and the struts along the distal regioncoupled to one another to define a closed shape along the distal regionof the ablation electrode.

In some implementations, at least some of the cells of the plurality ofcells can have a larger area in the uncompressed state of the ablationelectrode than in the compressed state of the ablation electrode.

In certain implementations, in the compressed state, the ablationelectrode can be deliverable through an 8 Fr sheath.

In some implementations, in the compressed state, strain in the ablationelectrode can be less than about ten percent.

In certain implementations, at least some of the plurality of cells canbe substantially diamond-shaped in the uncompressed state.

In some implementations, each end of each of the struts can be coupledto an end of another strut or to the distal end portion of the cathetershaft.

In certain implementations, the ablation electrode can have an outerportion and an inner portion opposite the outer portion and each cellcan extend from the outer portion to the inner portion.

In some implementations, the struts can be formed of nitinol.

In certain implementations, the plurality of cells can becircumferentially and axially disposed about the ablation electrode.

In some implementations, each of the struts can define a portion of atleast two cells.

In certain implementations, a combined area of the plurality of cellsalong an outer surface of the ablation electrode can be greater than acombined surface area of the struts along the outer surface of theablation electrode.

In some implementations, some of the struts can be wider than other onesof the struts. For example, at least some of the wider struts can bemechanically fixed relative to the distal portion of the catheter shaft.Additionally, or alternatively, the other ones of the struts are movablerelative to the distal portion of the catheter shaft.

In certain implementations, at least some of the struts include anon-uniform width along a length of the respective strut.

According to still another aspect, a catheter can include a cathetershaft, an irrigation element, and an ablation electrode. The cathetershaft can have a proximal end portion and a distal end portion. Theirrigation element can be positioned relative to the catheter shaft todirect irrigation fluid distal to the distal end portion of the cathetershaft. The ablation electrode can include a distal region and a proximalregion, the proximal region coupled to the distal end portion of thecatheter shaft. The distal region can include struts coupled to oneanother to define collectively a plurality of cells. Each cell in theplurality of cells can be bounded by at least four of the struts, andthe struts can be coupled to one another to define a closed shape alongthe distal region, the closed shape of the distal end region envelopingthe irrigation element.

In certain implementations, the catheter can further include a fastener(e.g., a rivet) coupling the struts to one another to define a closedshape along the distal end region. For example, the fastener can beformed of a first material and the struts are formed of a second, thefirst material different from the second material. Further, or instead,a portion of the struts can define respective eyelets through which thefastener extends to couple the portion of the struts to one another. Theeyelets can be, for example, aligned with one another. The fastener can,for example, extend through the eyelets at a distalmost position of theablation electrode. Additionally, or alternatively, the plurality ofcells can include a first set of cells and a second set of cells. Thefirst set of cells can be bounded by the portion of the struts definingrespective eyelets, the second set of cells can be bounded by the strutswithout eyelets, and the second set of cells can be bounded by fewerstruts than the first set of cells.

In some implementations, the catheter shaft can define a center axisextending from the proximal end portion to the distal end portion. Thecenter axis can extend, for example, through the fastener in the absenceof an external force applied to the ablation electrode.

In certain implementations, each end of the strut can be coupled to anend of at least one of the other struts or to the distal end portion ofthe catheter shaft.

In some implementations, at least one portion of the ablation electrodecan be resiliently flexible between a compressed state, in the presenceof an external force, and an uncompressed state, in the absence of anexternal force. For example, at least some of the cells of the pluralityof cells can have a larger area in the uncompressed state than in thecompressed state. As a further or alternative example, the ablationelectrode can be self-expandable from the compressed state to theuncompressed state. In certain instances, the ablation electrode can bedeliverable through an 8 Fr sheath. In some instances, in the compressedstate, strain in the ablation electrode is less than about ten percent.Further or instead, the ablation electrode can be bulbous in theuncompressed state.

In certain implementations, the struts can be formed of nitinol.

In some implementations, the plurality of cells can be circumferentiallyand axially disposed about the ablation electrode.

In some implementations, each of the struts can define a portion of atleast two cells.

According to another aspect, a method of forming a catheter can includeforming an ablation electrode having two open ends, the ablationelectrode including struts collectively defining a first set of cells, aportion of the struts having a first end region coupled to another oneof the struts and a second end region uncoupled from each of the otherstruts, inserting a fastener through the respective second end regionsof the portion of the struts to couple the second end regions to oneanother to define a second set of cells and to close one of the two openends of the ablation electrode, and coupling the ablation electrode to adistal end portion of a catheter shaft.

In certain implementations, the open end of the ablation electrode awayfrom the fastener can be coupled to the distal end portion of thecatheter shaft.

In some implementations, with the second end regions of the portion ofthe struts coupled to one another, the ablation electrode can beresiliently flexible between a compressed state, in the presence of anexternal force, and an uncompressed state, in the absence of an externalforce.

In certain implementations, the second end region of each respectivestrut of the portion of struts can define an eyelet and inserting thefastener through the respective second end regions of the portion ofstruts can include aligning the eyelets of the second end regions suchthat the fastener is inserted through the aligned eyelets.

In some implementations, forming the ablation electrode can includeremoving material from a flat sheet of material to form the first set ofcells. For example, removing material from the flat sheet of materialcan include one or more of laser cutting the flat sheet of material andchemically etching the flat sheet of material.

In certain implementations, forming the ablation electrode can includeremoving material from a tube of material to form the first set ofcells. For example, removing material from the tube of material includeslaser cutting the tube.

In some implementations, the ablation electrode can be formed ofnitinol.

According to still another aspect, the catheter can include a cathetershaft and an ablation electrode (e.g., formed of nitinol). The cathetershaft can have a proximal end portion and a distal end portion. Theablation electrode can be coupled to the distal end portion of thecatheter shaft and in electrical communication with an electrical powersource. The ablation electrode can include a deformable portionresiliently flexible between a compressed state and an uncompressedstate. The deformable portion can have less than about ±10 percentvariation in current density at 1 mm away in a medium of uniformconductivity from an outer portion of the deformable portion in theuncompressed state as current from the electrical power source movesthrough the deformable portion of the ablation electrode.

In certain implementations, in the uncompressed state, the maximumradial dimension of the deformable portion is at least 20 percentgreater than a maximum radial dimension of the catheter shaft. Forexample, in the compressed state, the deformable portion can bedeliverable through an 8 Fr sheath.

In some implementations, the deformable portion can be substantiallyspherical in the uncompressed state.

In certain implementations, at least the deformable portion of theablation electrode can include electropolished surfaces.

In some implementations, the deformable portion can include strutscollectively defining a plurality of cells, each cell extending from theouter portion of the deformable portion to an inner portion of thedeformable portion. For example, the area of at least some of the cellscan be larger in the uncompressed state than the area of the respectivecell in the compressed state.

In certain implementations, the catheter shaft can define a center axisextending from the proximal portion to the distal portion and thedeformable portion is symmetric about a plane including the center axis.

According to another aspect, a catheter includes a catheter shaft and anablation electrode. The catheter shaft can have a proximal end portionand a distal end portion. The ablation electrode can include a distalregion and a proximal region, the proximal region coupled to the distalend portion of the catheter shaft. The ablation electrode can beconnectable in electrical communication with an electrical power source.The ablation electrode can include struts collectively defining aplurality of cells, wherein open area of the cells of the plurality ofcells varies from the proximal region to the distal region of theablation electrode, and the struts defining the plurality of cells areelectrically conductive.

In certain implementations, a number of the cells along a meridian ofthe distal region can be less than a number of cells along a meridianpassing through a maximum radial dimension of the ablation electrode.

In some implementations, the number of cells along a meridian of theproximal region can be less than a number of cells along a meridianpassing through a maximum radial dimension of the ablation electrode.

In certain implementations, the struts defining the plurality of cellscan have a substantially uniform width.

In some implementations, the struts can include a first set of strutshaving a first width and a second set of struts having a second width,different from the first width, and the first set of struts are axiallyspaced from the second set of struts.

In certain implementations, at least some of the struts can have anon-uniform width along a respective length of the strut. For example,the at least some of the struts can have a width increasing along therespective length of the strut in a direction from the proximal regionto the distal region of the ablation electrode.

According to still another aspect, a catheter can include a cathetershaft and an ablation electrode. The catheter shaft has a proximal endportion and a distal end portion, and the ablation electrode is coupledto the distal end portion of the catheter shaft. The ablation electrodeincludes a deformable portion resiliently flexible between a compressedstate and an uncompressed state, the deformable portion in theuncompressed state positionable at multiple different angles relative totissue at a treatment site, and, for the same amount of ablation energydelivered from the deformable portion to the tissue at a given amount ofpressure between the deformable portion and the tissue, the deformableportion generating lesions of substantially similar size at each of themultiple different angles.

In certain implementations, the multiple different angles can include anaxial direction defined by the catheter shaft and a lateral directionperpendicular to the axial direction.

In some implementations, the lesions can correspond to each of themultiple different angles have similar depth and similar width at eachof the multiple different angles.

In certain implementations, the lesions can correspond to each of themultiple different angles have a depth varying by less than about ±30percent. For example, the lesions can correspond to each of the multipledifferent angles have a depth varying by about ±20 percent.

In some implementations, the deformable portion in the uncompressedstate can have a maximum lateral dimension at least 20 percent greaterthan a maximum lateral dimension of the catheter shaft.

In certain implementations, the deformable portion includes an openframework through which fluid is movable through the framework to coolthe deformable portion.

According to another aspect, a cardiac catheter includes a cathetershaft, a center electrode, enclosure, and surface electrodes. Thecatheter shaft has a proximal end portion and a distal end portion. Thecenter electrode is coupled to the distal end portion of the cathetershaft. The enclosure is coupled to the distal end portion of thecatheter shaft, the enclosure resiliently flexible in response toexternal force, and the enclosure enveloping the center electrode in theabsence of external force. The surface electrodes can be disposed alongthe enclosure and spaced apart from the center electrode in the absenceof external force applied to the enclosure.

In certain implementations, in the absence of external force applied tothe enclosure, each surface electrode can be spaced from the centerelectrode by a distance greater than about 2 mm and less than about 6mm.

In some implementations, independent of orientation of the enclosurerelative to tissue, the enclosure can make initial contact with thetissue before the center electrode makes initial contact with thetissue.

In certain implementations, in the absence of external force applied tothe enclosure, the surface electrodes can be noncoplanar relative to oneanother.

In some implementations, the enclosure can be an ablation electrode.

In certain implementations, each surface electrode can be electricallyisolated from the enclosure.

In some implementations, the enclosure can include an outer portionopposite an inner portion, the enclosure defining a plurality of cellsextending from the outer portion to the inner portion.

In certain implementations, the center electrode can be in fluidcommunication with the outer portion of the enclosure through theplurality of cells.

In some implementations, each surface electrode can be disposed alongthe outer portion of the enclosure.

In certain implementations, each surface electrode can be disposed alongthe inner portion of the enclosure.

In some implementations, each surface electrode can extend through theenclosure, from an outer portion of the enclosure to an inner portion ofthe enclosure.

In certain implementations, the enclosure, in the absence of externalforce, can have a maximum radial dimension greater than a maximum radialdimension of the distal end portion of the catheter shaft. For example,the maximum radial dimension of the enclosure can be greater than themaximum radial dimension of the distal end portion of the catheter shaftby at least about 20 percent.

In some implementations, in the absence of external force applied to theenclosure, at least a portion of the enclosure can be substantiallyspherical.

In certain implementations, the center electrode can be spaced distallyfrom the distal end portion of the catheter shaft.

In some implementations, the center electrode can be disposed on anirrigation element in fluid communication with the catheter shaft.

In certain implementations, the center electrode can be disposedsubstantially along a center axis defined by the catheter shaft.

According to another aspect, a system can include a catheter shaft, acenter electrode, an enclosure, surface electrodes, and a catheterinterface unit. The catheter shaft has a proximal end portion and adistal end portion. The center electrode is coupled to the distal endportion of the catheter shaft. Th enclosure is coupled to the distal endportion of the catheter shaft, the enclosure resiliently flexible inresponse to an external force, and the enclosure enveloping the centerelectrode in the absence of the external force. The surface electrodesare disposed along the enclosure and spaced apart from the centerelectrode in the absence of external force applied to the enclosure. Thecatheter interface unit includes a graphical user interface, one or moreprocessors and a non-transitory, computer readable storage medium havingstored thereon computer executable instructions for causing the one ormore processors to acquire a plurality of electrograms, each respectiveelectrogram based on a difference between a first electrical signal anda second electrical signal, the first electrical signal from arespective one of the surface electrodes, and the second electricalsignal from the center electrode, and display a representation of atleast one of the plurality of electrograms on the graphical userinterface.

In certain implementations, the computer readable storage medium furthercan have stored thereon computer executable instructions for causing theone or more processors to determine a voltage map of a heart associatedwith the plurality of electrograms, the voltage map based at least inpart on the plurality of electrograms. Additionally, or alternatively,the non-transitory, computer readable storage medium can have storedthereon computer executable instructions for causing the one or moreprocessors to display the voltage map on the graphical user interface.

According to still another aspect, a method of determining electricalactivity associated with a heart of a patient can include receiving afirst electrical signal from a center electrode of a cardiac catheter,for surface electrodes disposed on an enclosure enveloping the centerelectrode, receiving a plurality of second electrical signals, eachrespective second electrical signal associated with one of the surfaceelectrodes, and determining a plurality of electrograms, eachelectrogram based on a difference between a respective one of the secondelectrical signals and the first signal.

In certain implementations, the center electrode can be at least about 2mm and less than about 6 mm from each of the surface electrodes in theabsence of a force applied to the enclosure enveloping the centerelectrode.

In some implementations, the method can further include sending arepresentation of one or more of the electrograms to a graphical userinterface.

In certain implementations, the method can further include determining avoltage map of the heart based at least in part on the plurality ofelectrograms.

In some implementations, the method can further include sendingelectrical energy to an irrigation element of the cardiac catheter,wherein the center electrode is disposed along the irrigation element,and the electrical energy to the irrigation element reduces noise on oneor more of the first electrical signal and the plurality of the secondelectrical signals.

According to still another aspect, a method of treating a cardiaccondition includes moving a distal end region of a catheter shaft towarda cavity of a heart of a patient, for an enclosure coupled to thecatheter shaft, expanding the enclosure such that surface electrodesdisposed on the enclosure move in a direction away from a centerelectrode enveloped by the enclosure and coupled to the catheter shaft,and selectively treating tissue of the cavity based on a plurality ofelectrograms, each electrogram based on a difference between a firstelectrical signal from the center electrode and a second electricalsignal from at least one surface electrode disposed on the enclosure.

In certain implementations, selectively treating the tissue of thecavity can include delivering ablation energy to the tissue of thecavity.

In some implementations, delivering ablation energy to the tissue of thecavity includes delivering ablation energy to the enclosure upon whichthe surface electrodes are disposed.

Embodiments can include one or more of the following advantages.

In certain implementations, irrigation holes of an irrigation elementare directed toward an inner portion of the ablation electrode. Thisconfiguration can facilitate cooling the ablation electrode through acombination of irrigation fluid and blood flow past the inner portion ofthe ablation electrode. For example, directing irrigation fluid towardthe inner portion of the ablation electrode can facilitate the movementof blood in the space between the introduction of the irrigation fluidand the inner portion of the ablation electrode. Thus, as compared toclosed cooling configurations, implementations including the irrigationsholes directed toward the inner portion of the ablation electrode canimprove local cooling at the ablation electrode and/or reduce thelikelihood of blood clot or charring at the treatment site.

In some implementations, an ablation electrode is expandable from acompressed state to an uncompressed state. As compared to ablationelectrodes that are not expandable, expandable ablation electrodes ofthe present disclosure can be delivered through relatively small sheaths(e.g., 8 French sheaths) while still having a large surface area throughwhich energy can be safely delivered to tissue to create lesions in thetissue of the patient. Also, or instead, expandable ablation electrodesof the present disclosure can have an open area through which blood canflow during treatment. As compared to ablation electrodes that areimpervious to the movement of blood, the expandable ablation electrodesof the present disclosure have a reduced impact on the natural movementof blood and, thus, a reduced impact on cooling afforded by the naturalmovement of blood past the treatment site.

In certain implementations, sensors are disposed on a deformable portionof an expandable ablation electrode, and deformation of the deformableportion of the ablation electrode can be detected in one or moredirections using the sensors. In general, such a configuration ofsensors can provide information about the amount and direction ofcontact force exerted on tissue by the expandable electrode which, bybeing expandable, can have a larger surface area than a non-expandableelectrode deliverable through a sheath of a given size. Morespecifically, because the deformation of the deformable portion can bereproducible (e.g., substantially linear in some cases) as a function offorce (e.g., over a range of forces associated with an ablationprocedure), deformation detected by the sensors can be useful asfeedback regarding the amount and direction of force applied to tissueby the expandable ablation electrode having a large surface area. Thus,in combination with or in addition to the large surface area afforded bythe expandable ablation electrode, the deformation detectable by thesensors regarding the degree and/or direction of contact between theexpandable ablation electrode and tissue can, for example, facilitateapplication of appropriate force and the safe application of energy totissue.

In some implementations, an ablation electrode includes a deformableportion resiliently flexible between a compressed state and anuncompressed state, the deformable portion having a substantiallyuniform current density (e.g., less than about ±10 percent variation incurrent density at 1 mm away from an outer portion of the deformableportion) as current from an electrical power source moves through thedeformable portion in the uncompressed state. Such a substantiallyuniform distribution of current density can facilitate reliable andrepeatable creation of large lesions with an expandable electrode.Additionally, or alternatively, the substantially uniform distributionof current density in an expandable electrode can facilitate forminglarge lesions in a manner that is substantially independent oforientation of the expandable electrode relative to the tissue.

Other aspects, features, and advantages will be apparent from thedescription and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of an ablation system during anablation treatment.

FIG. 2 is a perspective view of a catheter of the ablation system ofFIG. 1.

FIG. 3 is a perspective view of a distal end portion of the catheter ofthe ablation system of FIG. 1.

FIG. 4 is a cross-sectional perspective view along cross-section A-A ofFIG. 3.

FIG. 5 is a schematic representation of a jet of irrigation fluid movingfrom an irrigation element to an inner portion of an ablation electrodeof the catheter of FIG. 2.

FIG. 6 is a side view of an ablation electrode of the ablation system ofFIG. 1.

FIG. 7 is a perspective view of the ablation electrode of the ablationsystem of FIG. 1.

FIG. 8 is a cross-sectional view, taken along line B-B in FIG. 7, of theablation electrode of the ablation system of FIG. 1.

FIG. 9 is an exemplary graph of force as a function of displacement of adeformable portion of the ablation electrode of the ablation system ofFIG. 1.

FIG. 10 is a perspective view of sensors and the ablation electrode ofthe ablation system of FIG. 1, with the sensors shown mounted to theablation electrode.

FIG. 11 is a perspective view of a sensor of the ablation system of FIG.1.

FIGS. 12A-12C are schematic representations of a method of forming theablation electrode of the ablation system of FIG. 1.

FIGS. 13A-13E are schematic representations of a method of inserting thecatheter of FIG. 2 into a patient.

FIGS. 14A-C are schematic representations of a method of positioning theablation electrode of the ablation system of FIG. 1 at a treatment siteof a patient.

FIGS. 15A-B are schematic representations of a method of irrigating theablation electrode of the ablation system of FIG. 1.

FIG. 16 is a schematic representation of a side view of a helicalirrigation element of a catheter of an ablation system.

FIG. 17 is a side view of an irrigation element of a catheter of anablation system, the irrigation element including a porous membrane.

FIG. 18 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 19 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 20 is a cross-sectional perspective view along cross-section D-D ofFIG. 19.

FIG. 21 is a perspective view of a distal end portion of a catheter ofan ablation system.

FIG. 22 is a cross-sectional side view of the catheter of FIG. 21 alongcross-section E-E. of FIG. 21.

FIG. 23 is a perspective view of an irrigation element of the catheterof FIG. 21.

FIG. 24 is a perspective view of a tube for forming the irrigationelement shown in FIG. 23.

FIG. 25 is a schematic representation of placement of a sensor on anablation electrode of the catheter of FIG. 21.

FIG. 26 is a schematic representation of a trajectory around an outersurface of an ablation electrode of the catheter of FIG. 21, thetrajectory used to present simulation results of current densityassociated with the ablation electrode.

FIG. 27 is a graph of percentage change in simulated current densityalong the trajectory shown in FIG. 26, at a fixed distance of 1 mm froman outer surface of the ablation electrode.

FIG. 28 is a graph of depth and width of lesions applied to chickenbreast meat using the ablation electrode of FIG. 21 in axial and lateralorientations relative to the chicken breast meat.

FIG. 29 is a side view of a deformable portion of an ablation electrode,the deformable portion of the ablation portion including a substantiallyconical proximal portion.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

The present disclosure is generally directed to systems and methods ofablating tissue of a patient during a medical procedure being performedon an anatomic structure of the patient. By way of non-limiting exampleand for the sake of clarity of explanation, the systems and methods ofthe present disclosure are described with respect to ablation of tissuein a heart cavity of the patient as part of an ablation treatmentassociated with the treatment of cardiac arrhythmia. However, it shouldbe appreciated that, unless otherwise specified, the systems and methodsof the present disclosure can be used for any of various differentmedical procedures, such as procedures performed on a hollow anatomicstructure of a patient, in which ablation of tissue is part of a medicaltreatment.

As used herein, the term “physician” should be considered to include anytype of medical personnel who may be performing or assisting a medicalprocedure.

As used herein, the term “patient” should be considered to include anymammal, including a human, upon which a medical procedure is beingperformed.

FIG. 1 is a schematic representation of an ablation system 100 during acardiac ablation treatment being performed on a patient 102. Theablation system 100 includes a catheter 104 connected, via an extensioncable 106, to a catheter interface unit 108. The catheter interface unit108 can be a computing device that includes a processing unit 109 a, anon-transitory, computer readable storage medium 109 b, and a graphicaluser interface 110. The processing unit 109 a can be a controllerincluding one or more processors, and the storage medium 109 b can havestored thereon computer executable instructions for causing the one ormore processors of the processing unit 109 a to carry out one or moreportions of the various methods described herein, unless otherwiseindicated or made clear from the context.

A mapping system 112, a recording system 111, an irrigation pump 114,and a generator 116 can be connected to the catheter interface unit 108.The irrigation pump 114 can be removably and fluidly connected to theablation catheter 104 via fluid line 115. The generator 116 can also, orinstead, be connected, via one or more of wires 117, to one or morereturn electrodes 118 attached to the skin of the patient 102. Therecording system 111 can be used throughout the ablation treatment, aswell as before or after the treatment. The mapping system 112 can beused prior to and/or during an ablation treatment to map the cardiactissue of the patient 102 and determine which region or regions of thecardiac tissue require ablation.

Referring now to FIGS. 2-4, the catheter 104 can include a handle 120, acatheter shaft 122, an ablation electrode 124, sensors 126, and anirrigation element 128. The handle 120 is coupled to a proximal endportion 130 of the catheter shaft 122, and a distal end portion 132 ofthe catheter shaft 122 can be coupled to the irrigation element 128 andto the ablation electrode 124, which supports the sensors 126 in someimplementations. The handle 120 can, further or instead, be coupled tothe fluid line 115 and to one or more of the wires 117 for delivery ofirrigation fluid and electrical energy, respectively, along the cathetershaft 122, to the ablation electrode 124.

As described in further detail below, in a deployed state of theablation electrode 124, irrigation fluid exits irrigation holes 134defined by the irrigation element 128 and is directed toward an innerportion 136 of the ablation electrode 124 while an outer portion 138(opposite the inner portion 136) of the ablation electrode 124 is incontact with tissue as part of an ablation treatment. Spacing betweenthe irrigation holes 134 and the inner portion 136 of the ablationelectrode 124 can facilitate heat transfer between the irrigation fluidand the ablation electrode 124. For example, in the spacing between theirrigation holes 134 and the inner portion 136 of the ablation electrode124, the respective jets of irrigation fluid can develop turbulentcharacteristics. Without wishing to be bound by theory, it is believedthat, as compared to non-turbulent or less turbulent flow of irrigationfluid, increased turbulence can improve local heat transfer from theablation electrode 124 (e.g., from the inner portion 136 of the ablationelectrode 124) to the irrigation fluid. Additionally, or alternatively,blood can flow through the spacing between the irrigation holes 134 andthe inner portion 136 of the ablation electrode 124. As compared toconfigurations in which the flow of blood away from the treatment siteis impeded, the flow of blood through the spacing between the irrigationholes 134 and the inner portion 136 of the ablation electrode 124 can,additionally or alternatively, improve further the local heat transferfrom the outer portion 138 of the ablation electrode 124. In general, itshould be appreciated that such improved local heat transfer can reducethe likelihood of blood clot or charring. As used herein, the term“holes” should be understood to include any size and shape of discreteorifice having a maximum dimension and through which fluid can flow and,thus, should be understood to include any manner and form ofsubstantially geometric shapes (e.g., substantially circular shapes)and, also or instead, substantially irregular shapes, unless otherwisespecified or made clear from the context.

As also described in further detail below, the ablation electrode 124can include a coupling portion 140 and a deformable portion 142. As usedherein, the terms “expandable” and “deformable” are usedinterchangeably, unless otherwise specified or made clear from thecontext. Thus, for example, it should be understood that the deformableportion 142 is expandable unless otherwise specified.

The coupling portion 140 is secured to the distal end portion 132 of thecatheter shaft 122, and the deformable portion 142 can extend distallyfrom the coupling portion 140. The deformable portion 142 of theablation electrode 142 can be deformed for delivery (e.g., through anintroducer sheath, such as an 8F introducer sheath) and expanded at atreatment site to have a cross-sectional dimension larger than across-sectional dimension of the catheter shaft 122. As compared tosmaller ablation electrodes, the ablation electrode 124 can providewider lesions within a shorter period of time, facilitating the creationof a pattern of overlapping lesions (e.g., reducing the likelihood ofarrythmogenic gaps, and reducing the time and number of lesions requiredfor an overlapping pattern, or both). Additionally, or alternatively, alarger tip can facilitate the delivery of more power for providing widerand deeper lesions.

Further, in an expanded state, the deformable portion 142 of theablation electrode 124 is deformable upon sufficient contact force withtissue, and the shape and extent of the deformation can be detectedbased, at least in part, upon signals received from the sensors 126 onthe deformable portion 142 of the ablation electrode 124. As describedin greater detail below, the sensors 126 can be used in one or moremodes of parameter measurement and, for example, can include one or moreof an electrode, a thermistor, an ultrasound transducer, and an opticalfiber. Additionally, or alternatively, the deformable portion 142 can beradiopaque such that deformation of the deformable portion 142 as aresult of contact with tissue is observable, for example, through X-rayor similar visualization techniques. The detection and/or observation ofthe deformation of the deformable portion 142 of the ablation electrode124 can, for example, provide improved certainty that an intendedtreatment is, in fact, being provided to tissue. It should beappreciated that improved certainty of positioning of an ablationelectrode with respect to tissue can reduce the likelihood of gaps in alesion pattern and, also or instead, can reduce the time and number ofablations otherwise required to avoid gaps in a lesion pattern.

The handle 120 can include a housing 145 and an actuation portion 146.In use, the actuation portion 146 can be operated to deflect the distalend portion 132 of the catheter shaft 122 to facilitate positioning theablation electrode 124 into contact with tissue at a treatment site. Thehandle 120 can include a fluid line connector 148 (e.g., a luerconnector) and an electrical connector 149. The fluid line 115 can beconnectable to the fluid line connector 148 and, in use, irrigationfluid (e.g., saline) can be delivered from the irrigation pump 114 tothe catheter 104 where, as described in further detail below, theirrigation fluid is ultimately deliverable through the irrigation holes134 of the irrigation element 128 to the inner portion 136 of theablation electrode 124. The extension cable 106 is connectable to theelectrical connector 149. In use, electrical energy can be deliveredfrom the generator 116 to the catheter 104 where, as described infurther detail below, the electrical energy is ultimately deliverable tothe ablation electrode 124 to ablate tissue in contact with the outerportion 138 of the ablation electrode 124.

The handle 120 can be attached to the proximal end portion 130 of thecatheter shaft 122 through any of various techniques, including one ormore of adhesive bonds, thermal bonds, and mechanical connections.

The catheter shaft 122 defines a lumen 151 extending from the proximalend portion 130 of the catheter shaft 122 to the distal end portion 132of the catheter shaft 122. The lumen 151 can be in fluid communicationwith the irrigation pump 114, via the fluid line 115 and the fluid lineconnector 148 of the handle 120, such that irrigation fluid can bepumped from the irrigation pump 114 to the irrigation holes 134 definedby the irrigation element 128. The catheter shaft 122 can also, orinstead, include electrical wires (such as any one or more of the wires117 shown in FIG. 1) extending along the catheter shaft 122 to carrysignals between the sensors 126 and the catheter interface unit 108 andto carry electrical power from the generator 116 to the ablationelectrode 124.

The catheter shaft 122 can be formed of any of various differentbiocompatible materials that provide the catheter shaft 122 withsufficient sturdiness and flexibility to allow the catheter shaft 122 tobe navigated through blood vessels of a patient. Examples of suitablematerials from which the catheter shaft 122 can be formed includepolyether block amides (e.g., Pebax®, available from Arkema of Colombes,France), nylon, polyurethane, Pellethane® (available from The LubrizolCorporation of Wickliffe, Ohio), and silicone. In certainimplementations, the catheter shaft 122 includes multiple differentmaterials along its length. The materials can, for example, be selectedto provide the catheter shaft 122 with increased flexibility at thedistal end, when compared to the proximal. The catheter shaft 122 canalso, or instead, include a tubular braided element that providestorsional stiffness while maintaining bending flexibility to one or moreregions of the catheter shaft 122. Further, or in the alternative, theshaft material can include radiopaque agents such as barium sulfate orbismuth, to facilitate fluoroscopic visualization.

The catheter shaft 122 can further include pull wires (not shown)mechanically coupled (e.g., via a ring secured to the catheter shaft122) to the distal end portion 132 of the catheter shaft 122 andmechanically coupled to the actuation portion 146 of the handle 120, asis well known in the art. During use, tension may be applied to thewires to deflect the distal end portion 132 of the catheter shaft 122 tosteer the catheter shaft 122 toward a treatment site.

The irrigation element 128 can include a stem 154 and a bulb 156. Thestem 154 can be coupled to the distal end portion 132 of the cathetershaft 122 in fluid communication with the lumen 151 of the cathetershaft 122 and, ultimately, with the irrigation pump 114. The bulb 156defines the irrigation holes 134 and is in fluid communication with thestem 154. Accordingly, irrigation fluid can pass through the lumen 151,through the stem 154, and can exit the irrigation element 128 throughthe irrigation holes 134 defined by the bulb 156.

The stem 154 can be substantially rigid and extend from the distal endportion 132 of the catheter shaft 122 in a direction having a distalcomponent and/or a radial component. For example, a radial extent of thestem 154 can direct irrigation fluid from an off-center position of thelumen 151 to a position along a center axis defined by the cathetershaft 122. Additionally, or alternatively, a distal extent of the stem154 can facilitate clearance of the catheter shaft 122 such that aportion of the irrigation holes 134 directed in the proximal directionhave a substantially unobstructed path to a portion of the inner portion136 of the ablation electrode 124 that is proximal to the irrigationelement 128. Thus, more generally, it should be understood that the sizeand shape of one or more of the stem 154, the bulb 156, and theirrigation holes 134 can be varied to achieve desired directionality ofthe irrigation fluid toward the inner portion 136 of the ablationelectrode 124.

The bulb 156 can be substantially rigid and, in certain implementations,formed of the same material as the stem 154. Additionally, oralternatively, the bulb 156 can be substantially spherical to facilitatedirecting irrigation fluid toward substantially the entire inner portion136 of the ablation electrode 124. It should be appreciated, however,that the bulb 156 can be any of various different shapes that facilitatemulti-directional dispersion of irrigation fluid toward the innerportion 136 of the ablation electrode 124.

In certain implementations, the irrigation holes 134 can be spacedcircumferentially and axially along the irrigation element. For example,the irrigation holes 134 can be spatially distributed along the bulb 156with at least a portion of the irrigation holes 134 arranged to directirrigation fluid in a distal direction with respect to the ablationelectrode 124 and at least a portion of the irrigation holes 134arranged to direct irrigation fluid in a proximal direction with respectto the ablation electrode 124. More generally, the irrigation holes 134can be distributed to produce a relatively uniform dispersion ofirrigation fluid along the inner portion 136 of the ablation electrode124 enveloping the irrigation element 128.

The overall radial extent of the irrigation element 128 can be less thanthe outer diameter of the catheter shaft 122. For example, theirrigation element 128 can remain in the same orientation in a deliveryconfiguration of the catheter 104 to the treatment and during treatmentat the treatment site while, as described in further detail below, theablation electrode 124 expands from a compressed state during deliveryto an expanded state during treatment at the treatment site. As alsodescribed in further detail below, the fixed orientation of theirrigation element 128 can facilitate using the irrigation element 128to act as a sensor or to carry a sensor. For example, a sensor can beadded to the irrigation element 128 to act as a sensor, in cooperationwith the sensors 126 such that the sensor on the irrigation element 128can act as a center electrode and the sensors 126 can act as surfaceelectrodes, as described in greater detail below.

While the irrigation element 128 can extend distal to the catheter shaft122, distal extent of the irrigation element 128 can be limited by theinner portion 136 of the ablation electrode 124. For example, theirrigation element 128 can be spaced relative to the inner portion 136of the ablation electrode 124 such that the irrigation holes 134 directirrigation fluid toward the inner portion 136 of the ablation electrode124 in an expanded state. In particular, given that the deformableportion 142 of the ablation electrode 124 is intended to contact tissueduring ablation, the irrigation holes 134 can be oriented toward thedeformable portion 142 of the ablation electrode 124 to direct fluidtoward the inner portion 136 of the ablation electrode 124 along thedeformable portion 142 in contact with the tissue. Directing theirrigation fluid toward the deformable portion 142 of the ablationelectrode 124 in this way can, for example, reduce the likelihood ofunintended tissue damage resulting from the ablation treatment.

Referring now to FIG. 5, a schematic representation of a jet 158 ofirrigation fluid exiting one of the irrigation holes 134 and movingtoward the inner portion 136 of the ablation electrode 124 is shown justprior to impact between the jet 158 and the inner portion 136. Adistance “L” is a perpendicular distance between the irrigation hole 134and the inner portion 136 of the ablation electrode 124 when theablation electrode 124 is in an undeformed state (e.g., in the absenceof an external force applied to the ablation electrode 124). For thesake of clarity, a two-dimensional cross-section of a single jet isshown. However, it should be understood that, in use, a respectivethree-dimensional jet issues from each of the irrigation holes 134 andthe plurality of jets may interact with one another and/or with thepatient's blood, along the distance “L,” to create additional turbulenceat the inner portion 136 of the ablation electrode 124.

In implementations in which the irrigation holes 134 have a circularcross-section, the ratio of a maximum dimension “D” of each of theirrigation holes 134 to the respective distance “L” between therespective irrigation hole 134 and the inner portion 136 of the ablationelectrode 124 can be greater than about 0.02 and less than about 0.2(e.g., greater than about 0.03 and less than about 0.06). Given otherdesign considerations (e.g., manufacturability of hole sizes of theirrigation holes 134, acceptable pressure drop in the system, theinfluence of blood flow between the irrigation element 128 and theablation electrode 124, or a combination thereof), this range of ratioswill result in turbulent flow of irrigation fluid at the inner portion136 of the ablation electrode 124. Without wishing to be bound bytheory, it is believed that, as compared to configurations with laminarflow and/or less turbulent flow of irrigation fluid past the innerportion 136 of the ablation electrode 124, the turbulent flow ofirrigation fluid moving from the irrigation holes 134 to the innerportion 136 of the ablation electrode 124 results in increased heattransfer, which can reduce unintended tissue damage during ablation.

The size and number of the irrigation holes 134 defined by theirrigation element 128 are selected such that the pressure of irrigationfluid in the irrigation element 128 is sufficient to prevent blood fromentering the irrigation holes 134. For example, providing for somemargin of variation in pressure of the irrigation fluid, the size andnumber of the irrigation holes 134 defined by the irrigation element 128can be selected such that the pressure of the irrigation fluid in theirrigation element 128 is at least about 0.5 psi greater than thepressure of the blood of the patient 102. Further, in implementations inwhich the irrigation element 128 is expandable (e.g., a balloon), thepositive pressure difference between the irrigation fluid within theirrigation element 128 and the blood of the patient 102 can allow theirrigation element 128 to maintain an expanded shape. The size andnumber of the irrigation holes 134 can be, additionally oralternatively, selected to provide substantially uniform coverage of theirrigation fluid on the deformable portion 142 of the ablation electrode124.

In certain implementations, the irrigation holes 134 defined by theirrigation element 128 have a total open area of greater than about 0.05mm2 and less than about 0.5 mm2. In some implementations, the totalnumber of the irrigations holes 134 can be greater than about 50 andless than about 250 (e.g., about 200). In implementations in which theirrigation element 128 is substantially rigid (e.g., formed of stainlesssteel and/or platinum iridium), the irrigation holes 134 can be formedinto the irrigation element 128 using any one or more material removaltechniques known in the art, examples of which include drilling and theuse of a laser. In implementations in which the irrigation element 127is formed of an elastomer, the irrigation holes 134 can be formedthrough the use of a laser.

Referring now to FIGS. 1-11, the ablation electrode 124 is a continuousstructure that acts as one electrode in the monopolar electrodeconfiguration of the ablation system 100, shown in FIG. 1. It should beappreciated, however, that the ablation electrode 124 can includeelectrically isolated portions such that the ablation electrode 124includes two electrodes of a bipolar electrode configuration.

The ablation electrode 124 can have an outer diameter of greater thanabout 4 mm and less than about 16 mm (e.g., about 8 mm) and,additionally or alternatively, a thickness of greater than about 0.07 mmand less than about 0.25 mm (e.g., about 0.17 mm). In certainimplementations, the ablation electrode 124 can have greater than about50 percent open area and less than about 95 percent open area (e.g.,about 80 percent open area). As used herein, the percentage of open areaof the ablation electrode 124 should be understood to be the ratio ofthe area through which fluid can flow from the outer portion 138 of theablation electrode 124 to the surface area of a convex hull thatincludes the outer portion 138 of the ablation electrode 124 and thestructural elements defining the outer portion 138 of the ablationelectrode, with the ratio expressed as a percentage. It should beappreciated that the open area of the ablation electrode 124 canfacilitate the flow of irrigation fluid and blood through ablationelectrode 124 during treatment. As compared to ablation electrodes thatimpede the flow of blood, the open area of the ablation electrode 124can reduce the likelihood of local heating of blood at the treatmentsite as ablation energy is delivered to the tissue. It should beappreciated that the delivery of irrigation fluid to the inner portion136 of the ablation electrode 124 can augment the cooling that occursthrough the flow of only blood through the open area.

In general, it should be appreciated that the dimensions of the ablationelectrode 124, including the dimensions related to the diameter,thickness, and/or open area, can facilitate retraction of the ablationelectrode 124. That is, the force required to retract the ablationelectrode 124 into a sheath (e.g., at the end of a procedure) are suchthat the ablation electrode 124 can be retracted by a physician withoutrequiring assistance of a separate mechanism to provide a mechanicaladvantage. Further, or instead, the dimensions of the ablation electrode124 can facilitate adequate expansion of the electrode 124. For example,in instances in which the electrode 124 is formed of nitinol, theablation electrode 124 can be dimensioned such that, in the compressedstate (e.g., for delivery), strain in the ablation electrode 124 is lessthan about ten percent. As a more general example, the ablationelectrode 124 can be dimensioned such that the ablation electrode 124 iscompressible to a size suitable for delivery (e.g., through an 8 Frenchsheath) using a force that avoids, or at least limits, plasticdeformation of the material of the ablation electrode 124. It should beappreciated that avoiding, or at least limiting, plastic deformation inthis way can facilitate expansion of the ablation electrode 124 in apredictable manner (e.g., to a full extent) in the absence of an appliedforce.

The coupling portion 140 of the ablation electrode 124 can be directlyor indirectly mechanically coupled to the catheter shaft 122. Forexample, the coupling portion 140 can include struts 144 a directlycoupled to the catheter shaft 122 or coupled to a transition partcoupled to the catheter shaft 122. Each strut 144 a can include aportion extending parallel to the catheter shaft 122 with the couplingportion 140 coupled to the catheter shaft 122 along the portion of thestrut 144 a extending parallel to the catheter shaft 122. Alternatively,or in addition, the coupling portion 140 can include a complete ringdirectly or indirectly mechanically coupled to the catheter shaft 122.

The coupling portion 140 can be electrically coupled to the generator116 via one or more of the wires 117 (shown in FIG. 1) and/or otherconductive paths extending from the generator 116, along the length ofthe catheter shaft 122, and to the coupling portion 140. For example,the coupling portion 140 can be fitted into the distal end portion 132of the catheter shaft 122, connected to wires extending to the generator116, and potted within an adhesive in the distal end portion 132 of thecatheter shaft 122. In use, electrical energy provided at the generator116 can be delivered to the coupling portion 140 and, thus, to thedeformable portion 142 of the ablation electrode 124, where theelectrical energy can be delivered to tissue of the patient 102.

The deformable portion 142 of the ablation electrode 124 can includestruts 144 b mechanically coupled to one another at joints 141 a todefine collectively a plurality of cells 147 of the ablation electrode124. Additionally, or alternatively, the struts 144 b can bemechanically coupled to one another by a fastener 141 b. Accordingly,each end of the struts 144 b can be coupled to an end of another strut144 b, to the fastener 141 b, or a combination thereof to define thedeformable portion 142 of the ablation electrode 124. For example, thestruts 144 b along the deformable portion 142 of the ablation electrodecan be coupled to one another, to the fastener 141 b, or to acombination thereof to define a closed shape along the deformableportion 142. Also, or instead, at least some of the struts 144 b can becoupled to the struts 144 a to transition between the deformable portion142 and the coupling portion 140 of the ablation electrode 124. Incertain implementations, the struts 144 b can be coupled to the struts144 a such that the coupling portion 140 defines an open shape along thecoupling portion 140 to facilitate, for example, securing the struts 144a to the distal end portion 132 of the catheter shaft 122.

The catheter shaft 122 defines a center axis CL-CL extending from theproximal end portion 130 to the distal end portion 132 of the cathetershaft 122. The cells 147 can have a generally axial orientation relativeto the center axis CL-CL. For example, each of the cells 147 can have arespective symmetry plane passing through a distal end of the cell 147,a proximal end of the cell 147, and the center axis CL-CL. Such anorientation can advantageously preferentially expand and contract thecells 147 relative to the center axis CL-CL, which can facilitatecompressing the deformable portion 142 of the ablation electrode 124 toa size suitable for delivery to a treatment site.

The center axis CL-CL can, for example, extend through the fastener 141b in the absence of an external force applied to the ablation electrode.Such alignment of the fastener 141 b can facilitate, in certaininstances, location of the distal end portion 142 of the ablationelectrode 124 (e.g., by locating the fastener 141 b at a treatmentsite).

The fastener 141 b can be formed of a first material (e.g., a polymer)and the struts 144 b can be formed of a second material (e.g., anitinol) different from the first material. It should be appreciatedthat the material of the fastener 141 b can be selected for acombination of strength and electrical properties suitable formaintaining the struts 144 b coupled to one another while achieving acurrent density distribution suitable for a particular application. Theclosed shape of the deformable portion 142 can, for example, facilitatethe delivery of substantially uniform current density through theablation electrode 124 in a manner that, as compared to an electrodewith an open shape, is less dependent on the orientation of the ablationelectrode 124 relative to tissue, as described in greater detail below.

In general, each cell 147 can be defined by at least three struts 144 b.Also, or instead, each strut 144 b can define a portion of at least twoof the cells 147. The inner portion 136 of the ablation electrode 124can be in fluid communication with the outer portion 138 of the ablationelectrode 124 through the plurality of cells 147 such that, in use,irrigation fluid, blood, or a combination thereof can move through theplurality of cells 147 to cool the ablation electrode 124 and tissue inthe vicinity of the ablation electrode 124.

At least some of the plurality of cells 147 can be flexible in the axialand lateral directions such that the open framework formed by theplurality of cells 147 along the deformable portion 142 of the ablationelectrode 124 is similarly flexible. For example, at least some of theplurality of cells can be substantially diamond-shaped in theuncompressed state of the deformable portion 142 of the ablationelectrode 124. As used herein, substantially diamond-shaped includesshapes including a first pair of joints substantially aligned along afirst axis and a second pair of joints substantially aligned along asecond axis, different from the first axis (e.g., perpendicular to thefirst axis).

The flexibility of the open framework formed by the plurality of cells147 along the deformable portion 142 of the ablation electrode 124 can,for example, advantageously resist movement of the deformable portion142 in contact with tissue during a medical procedure. That is, thedeformable portion 142 can deform upon contact with tissue and thedeformable portion 142 can engage the tissue through one or more of thecells 147 to resist lateral movement of the deformable portion 142relative to the tissue. That is, as compared to a closed surface incontact with tissue, the deformable portion 142 will resist unintendedmovement (e.g., sliding with respect to the tissue) with which it is incontact. It should be appreciated that such resistance to movement canfacilitate, for example, more accurate placement of lesions.

The struts 144 a, 144 b can have dimensions that differ fromcorresponding dimensions of other ones of the struts 144 a, 144 b. Forexample, the struts 144 b can have a dimension (e.g., width) thatdiffers from a corresponding dimension of another one of the struts 144b. Varying dimensions of the struts 144 a, 144 b, for example, canfacilitate delivery of substantially uniform current density through thedeformable portion 142 of the ablation electrode 124, as described ingreater detail below. Additionally, or alternatively, the struts 144 acan be wider than the struts 144 b to facilitate fixing the struts 144 adirectly or indirectly to the distal end portion 132 of the cathetershaft 122.

In general, the struts 144 b can be dimensioned and arranged relative toone another for delivery of substantially uniform current densitythrough the deformable portion 142 of the ablation electrode 124, asdescribed in greater detail below. By way of non-limiting example, afirst set of the struts 144 b can have a first width, and a second setof the struts 144 b can have a second width, different from the firstwidth. Continuing with this example, the first set of the struts 144 bcan be axially spaced relative to the second set of the struts 144 b.Such axial distribution of the material of the struts can be useful, forexample, for achieving a desired current density profile (e.g., asubstantially uniform current density profile). As another non-limitingexample, at least some of the struts 144 b can have a non-uniform widthalong a length of the respective strut 144 b such that the amount ofmaterial along a given strut is varied, resulting in an associateddistribution in current density. For example, at least some of thestruts 144 b can include a width increasing along the length of therespective strut 144 b in a direction from a proximal region to a distalregion of the ablation electrode 124.

While dimensions of the struts 144 b can be varied to achieve a desiredcurrent density distribution along the deformable portion 142, it shouldbe appreciated that the distribution of current density is moregenerally characterized as being a function of the distribution of metalalong the deformable portion 142 of the ablation electrode 124. Becausethe metal of the struts 144 b defines the plurality of cells 147, itshould be further appreciated that the distribution of current densityis also related to the open area of the plurality of cells 147. Inparticular, maintaining a substantially constant ratio of open area ofthe cells 147 to the volume of material of the struts 144 defining theopen area of the cells 147, along each meridian of the deformableportion 142, can be a useful design guide for achieving a substantiallyuniform distribution of current density. However, maintaining such asubstantially constant ratio must be achieved while also satisfying thestructural requirements for forming the desired shape of the deformableportion 142. That is, any suitable solution for the arrangement of thestruts 144 b to form the plurality of cells 147 to produce substantiallyuniform current density must also satisfy the structural requirementsfor forming a desired shape of the deformable portion 142 (e.g., asubstantially spherical shape).

In general, a substantially uniform current distribution can be achievedalong a substantially spherical shape of the deformable portion 142through a pattern of struts 144 and cells 147 that varies from theproximal region to the distal region of the deformable portion 142. Forexample, a substantially uniform current distribution can be achievedwhile meeting the structural requirements of the desired shape of thedeformable portion 142 by varying one or more of the dimensions (e.g.,length, width, thickness) of the struts 144 b, the number of the struts144 b, and the number of the cells 147 along the deformable potion 142.Thus, for example, the struts 144 b can have a substantially uniformwidth and/or thickness while one or more of the number of the struts 144b and the number of cells 147 can be varied from the proximal region tothe distal region of the deformable portion 142. As an additional, oralternative example, the number of the cells 147 along a meridian of oneor both of a distal region and a proximal region of the deformableportion 142 can be less than a number of the cells 147 along a meridianpassing through a maximum radial dimension of the ablation electrode.

In general, the plurality of cells 147 can be disposed circumferentiallyand axially about the ablation electrode 124. More specifically, asdescribed in greater detail below, the plurality of cells 147 can bearranged about the ablation electrode 124 (e.g., along the deformableportion 142 of the ablation electrode 124) to facilitate contraction andexpansion of the deformable portion 142 and/or to facilitatesubstantially uniform distribution of current density along thedeformable portion 142.

Each cell 147 can be bounded. In particular, as used herein, a boundedcell 147 includes a cell entirely defined by the struts 144 b, thejoints 141 a, sensors 126 disposed along the struts 144 b or the joints141 a, or a combination thereof. As described in further detail below,the struts 144 b can be connected to one another at the joints 141 a aspart of a unitary or substantially unitary structure. Additionally, oralternatively, as also described in greater detail below, the struts 144b can be connected to one another through welds, fasteners, or othermechanical connections at one or more of the joints 141 a.

The struts 144 b can be movable relative to one another through flexingat the joints 141 a. More specifically, the struts 144 b can be flexiblerelative to one another to move the deformable portion 142 between acompressed state, in the presence of an external force, and anuncompressed state, in the absence of the external force. For example, amaximum radial dimension (alternatively referred to herein as a lateraldimension) of the ablation electrode can increase by at least a factorof 2 as the coupled struts 144 b move relative to one another totransition the ablation electrode 124 from a compressed state, in thepresence of external force, to an uncompressed state, in the absence ofexternal force. This ratio of increase in size is achieved through theuse of the open framework of cells 147 formed by the struts 144 b, whichmakes use of less material than would otherwise be required for a solidshape of the same size. Further, or instead, it should be appreciatedthat the ratio of the increase in size achieved through the use of theopen framework of cells 147 is useful for delivery to a treatment sitethrough an 8 French sheath while also facilitating the formation oflarge lesions at the treatment site.

Through flexing at the joints 141 a and associated movement of thestruts 144 b, the deformable portion 142 can be resiliently flexible inan axial direction relative to the catheter shaft 122 and/or in a radialdirection relative to the catheter shaft 122. Additionally, oralternatively, the deformable portion 142 can be expandable (e.g.,self-expandable) from the compressed state to the uncompressed state.For example, the struts 144 b can be biased to move in one or moredirections away from one another to self-expand the deformable portion142 from the compressed state to the uncompressed state. In certaininstances, the inner portion 136 of the ablation electrode 124 along thedeformable portion 142 can be closer in the compressed state than in theuncompressed state to at least a portion of a surface of the irrigationelement 128 and, thus, the inner portion 136 of the ablation electrode124 can move away from at least a portion of the surface of theirrigation element 128 as the deformable portion 142 is expanded fromthe compressed state to the uncompressed state. In certain instances,the inner portion 136 of the ablation electrode 124 along the deformableportion 142 can be closer in the compressed state than in theuncompressed state to at least a portion of a surface of the irrigationelement 128 and, thus, the inner portion 136 of the ablation electrode124 can move away from at least a portion of the surface of theirrigation element 128 as the deformable portion 142 is expanded fromthe compressed state to the uncompressed state.

In the uncompressed state, the struts 144 b, the joints 141 a, and thecells 147 together can form an open framework having a conductivesurface along the deformable portion 142 of the ablation electrode 124.For example, the open framework formed by the struts 144 b, the joints141 a, and the cells 147 can have greater than about 50 percent openarea along the outer portion 138 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in theuncompressed state. Continuing with this example, in the uncompressedstate, the combined open area of the cells 147 can be greater than thecombined area of the struts 144 b and the joints 141 a along the outerportion 138 of the ablation electrode 124. Further, or instead, at leastsome of the cells 147 can have a larger area in the uncompressed stateof the deformable portion 142 than in the compressed state of thedeformable portion 142.

More generally, the open area defined by the cells 147 can have amagnitude and spatial distribution sufficient to receive the struts 144b and, optionally the sensors 126, as the deformable portion 142collapses from the uncompressed state to the compressed state.Accordingly, it should be appreciated that the magnitude of the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can, among other things, be useful forvarying the degree of expansion of a deformable portion 142 of theablation electrode 124 relative to a delivery state in which thedeformable portion 142 is in a compressed state. That is, the ratio ofthe combined open area of the cells 147 to the combined area of thestruts 144 b and the joints 141 a can facilitate minimally invasivedelivery (e.g., delivery through an 8 Fr sheath) of the ablationelectrode 124.

By way of example, a maximum radial dimension of the ablation electrode124 can increase by at least a factor of 2 as the struts 144 b moverelative to one another to transition the ablation electrode 124 (e.g.,the deformable portion 142 of the ablation electrode 124) from acompressed state, in the presence of an external force (e.g., a radialforce), to an uncompressed state, in the absence of an external force.Additionally, or alternatively, the struts 144 b can be movable relativeto one another such that a maximum radial dimension of the deformableportion 142, in the uncompressed state, is at least about 20 percentgreater than a maximum radial dimension of the catheter shaft 122 (e.g.,greater than a maximum radial dimension of the distal end portion 132 ofthe catheter shaft 122). It should be appreciated that the extension ofthe deformable portion 142 beyond the maximum radial dimension of thecatheter shaft 122 can facilitate creation of a lesion having a largewidth, as compared to an ablation electrode constrained by a radialdimension of a catheter shaft.

In certain implementations, the ablation electrode 124 has a maximumaxial dimension that changes by less than about 33 percent (e.g., about20 percent) as the struts 144 b expand (e.g., self-expand) from theuncompressed state to the compressed state upon removal of an externalradial force applied to the ablation electrode 124.

At least some of the struts 144 b extend in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 (e.g., an axis defined by the proximal endportion 130 and the distal end portion 132 of the catheter shaft 122).That is, the struts 144 b extending in a direction having acircumferential dimensional component with respect to an axis defined bythe catheter shaft 122 are nonparallel to the axis defined by thecatheter shaft 122. In some implementations, at least some of the struts144 b include a non-uniform width along a length of the respective strut144 b. Because current density at a given point along the ablationelectrode 124 is a function of the amount of surface area at the givenpoint along the ablation electrode 124, the non-uniform width of a givenone of the struts 144 b can facilitate balancing current density toachieve a target current density profile along the deformable portion142 of the ablation electrode 124. As described in greater detail below,the circumferential extension and/or the non-uniform width along thelength of at least some of the struts 144 b can facilitate substantiallyuniform distribution of current density along the deformable portion 142during a medical procedure.

While a large surface area of the struts 144 b can be advantageous forthe delivery of energy to tissue, an upper boundary of the area of thestruts 144 b can be the geometric configuration that will allow thestruts 144 b to collapse into the compressed state (e.g., duringdelivery to the treatment site and/or during contact with tissue at thetreatment site) without interfering with one another. Additionally, oralternatively, the struts 144 b can be twisted towards the inner portion136 of the ablation electrode 124. It should be appreciated that, ascompared to struts that are not twisted, the twisted struts 144 b can bewider while still being collapsible into the compressed state withoutinterfering with one another. Further in addition or further in thealternative, an upper boundary of the area of the struts 144 b can bethe amount of open area of the deformable portion 142 that willfacilitate appropriate heat transfer (e.g., during ablation) at theablation electrode 124 through the movement of irrigation fluid and/orblood through the deformable portion 142.

As used herein, the uncompressed state of the deformable portion 142refers to the state of the deformable portion 142 in the absence of asubstantial applied force (e.g., an applied force less than about 5grams). Thus, the uncompressed state of the deformable portion 142includes a state of the ablation electrode 124 in the absence ofexternal forces. Additionally, the uncompressed state of the deformableportion 142 includes a state of the ablation electrode 124 in which asmall applied force (e.g., less an about 5 grams) is present, but isinsufficient to create a significant deformation in the deformableportion 142.

In the uncompressed state of the deformable portion 142, the ablationelectrode 124 can be bulbous. For example, in the uncompressed state,the deformable portion 142 can be a shape having symmetry in a radialdirection and/or an axial direction relative to the catheter shaft 122.For example, in the uncompressed state the deformable portion 142 can bean ellipsoidal shape such as, for example, a substantially sphericalshape (e.g., an arrangement of the struts 144 b, each strut 144 b havinga planar shape, relative to one another to approximate a sphericalshape). Additionally, or alternatively, in the uncompressed state, thedeformable portion 142 can be a symmetric shape (e.g., a substantiallyellipsoidal shape or another similar shape contained between a firstradius and a perpendicular second radius, the first radius and thesecond radius within 30 percent of one another in magnitude). Symmetryof the deformable portion 142 can, for example, facilitate symmetricdelivery of ablation energy to the tissue in a number of orientations ofthe deformable portion 142 relative to the tissue being ablated.

At least when the deformable portion 142 is in the uncompressed state,the deformable portion 142 can envelop the irrigation element 128 suchthat the irrigation element 128 directs irrigation fluid toward theinner portion 136 of the ablation electrode 124. Accordingly, inimplementations in which the deformable portion 142 is symmetric, theirrigation element 128 can provide a substantially uniform distributionof irrigation fluid along the inner portion 136 of the ablationelectrode 124, as the deformable portion 142 in the uncompressed stateenvelops the irrigation element 128.

In certain implementations, the largest cross-sectional dimension of thedeformable portion 142 in the uncompressed state is larger than thelargest cross-sectional dimension of the catheter shaft 122. Thus,because the deformable portion 142 is expandable to extend beyond thecatheter shaft 122, the deformable portion 142 can create a lesion thatis larger than the largest dimension of the catheter shaft 122 such thatthe resulting lesions are wider and deeper than lesions created byablation electrodes that do not expand. For example, in the uncompressedstate, the deformable portion 142 can be substantially circular at thelargest cross-sectional dimension of the deformable portion, and thecatheter shaft 122 can be substantially circular at the largestcross-sectional dimension of the catheter shaft 122. Thus, continuingwith this example, the outer diameter of the deformable portion 142 islarger than the outer diameter of the catheter shaft 122.

The compressed state of the ablation electrode 124, as used herein,refers to the state of the ablation electrode in the presence of a force(e.g., a force of about 5 grams or greater) sufficient to cause thedeformable portion 142 to flex (e.g., through flexing of one or more ofthe joints 141 a) to a significant extent. Thus, for example, thecompressed state of the ablation electrode 124 includes the reduced sizeprofile of the ablation electrode 124 during introduction of thecatheter 104 to the treatment site, as described in further detailbelow. The compressed state of the ablation electrode 124 also includesone or more states of deformation and/or partial deformation resultingfrom an external force exerted along one or more portions of thedeformable portion 142 of the ablation electrode 124 as a result ofcontact between the deformable portion 142 and tissue at the treatmentsite.

The compressed state of the ablation electrode 124 can have apredetermined relationship with respect to an applied force. Forexample, the compressed state of the ablation electrode 124 can have asubstantially linear (e.g., within ±10 percent) relationship withapplied forces in the range of forces typically applied during anablation procedure (e.g., about 1 mm deformation in response to 60 gramsof force). It should be appreciated that such a predeterminedrelationship can be useful, for example, for determining the amount ofapplied force on the ablation electrode 124 based on a measured amountof deformation of the ablation electrode 124. That is, given thepredetermined relationship between deformation of the ablation electrode124 and an amount of an applied force, determining the amount ofdeformation of the ablation electrode 124 can provide an indication ofthe amount of force being applied by the ablation electrode 124 ontissue at the treatment site. As such, the determined amount ofdeformation of the ablation electrode 124 can be used, for example, asfeedback to control the amount of force applied to tissue at thetreatment site. Methods of determining the amount of deformation of theablation electrode 124 are described in greater detail below.

FIG. 9 is a graph of an exemplary relationship between force anddisplacement for different amounts of force applied to the deformableportion 142 of the ablation electrode 124. The deformable portion 142 ofthe ablation electrode 124 can have different force-displacementresponses, depending on the direction of the force applied to thedeformable portion 142 of the ablation electrode 124. For example, asshown in the exemplary relationship in FIG. 9, the deformable portion142 of the ablation electrode 124 can have an axial force-displacementresponse 143 a and a lateral force-displacement response 143 b. That is,the response of the deformable portion 142 to the application of forcecan depend on the direction of the applied force. In the specificexample of FIG. 9, the deformable portion 142 can be stiffer in theaxial direction than in the lateral direction.

In general, the axial force-displacement 143 a and the lateralforce-displacement response 143 b can be reproducible and, thus, theamount of force applied to the deformable portion 142 of the ablationelectrode 124 in the axial and/or lateral direction can be reliablydetermined based on respective displacement of the deformable portion142. Accordingly, as described in greater detail below, the determineddisplacement of the deformable portion 142 can be used to determine theamount and direction of force applied to the deformable portion 142.More generally, because the deformable portion 142 is movable between acompressed state and an uncompressed state in a reproducible manner inresponse to applied force, the deformable portion 142 of the ablationelectrode can be useful as a contact force sensor and, thus, canfacilitate application of appropriate force during ablation treatment.

In certain implementations, at least a portion of the ablation electrode124 is radiopaque, with the deformable portion 142 observable throughthe use of fluoroscopy or other similar visualization techniques. Forexample, the deformable portion 142 of the ablation electrode 124 can beradiopaque such that fluoroscopy can provide an indication of thedeformation and/or partial deformation of the deformable portion 142and, therefore, provide an indication of whether the deformable portion142 is in contact with tissue.

A material for forming the ablation electrode 124 can include nitinol,which is weakly radiopaque and is repeatably and reliably flexiblebetween a compressed state and an uncompressed state. Additionally, oralternatively, the material for forming the ablation electrode 124 canbe coated with one or more of gold or tantalum. Thus, continuing withthis example, the deformable portion 142 of the ablation electrode 124(e.g., the struts 144 b) can be formed of nitinol, either alone orcoated, such that ablation energy is delivered through the nitinolforming the deformable portion 142 for delivery to tissue to createlesions.

As described in further detail below, the deformation and/or partialdeformation of the deformable portion 142 in the compressed state can beadditionally, or alternatively, detected by the sensors 126 to providefeedback regarding the extent and direction of contact between thedeformable portion 142 of the ablation electrode 124 and the tissue atthe treatment site.

Referring now to FIGS. 10 and 11, the sensors 126 can be mounted alongthe deformable portion 142 of the ablation electrode 124. Each sensor126 can be electrically insulated from the ablation electrode 124 andmounted on one of the struts 144 b of the deformable portion 142. Forexample, each sensor 126 can be mounted to the deformable portion 142using a compliant adhesive (e.g., a room temperature vulcanized (RTV)silicone), any of various different mechanical retaining features (e.g.,tabs) between the sensor 126 and the ablation electrode 124, and/ormolding or overmolding of the sensor 126 to the ablation electrode 124.Because the struts 144 b do not undergo significant flexing as thedeformable portion 142 moves between the compressed state and theuncompressed state, mounting the sensors 126 on the struts 144 b canreduce physical strain on the sensors 126, as compared to mounting thesensors 126 on sections of the deformable portion 142 that experiencelarger amounts of flexing as the deformable portion 142 moves betweenthe compressed state and the uncompressed state.

Wires 148 extend from each sensor 126, along the inner portion 136 ofthe ablation electrode 124, and into the catheter shaft 122 (FIG. 2).The wires 148 are in electrical communication with the catheterinterface unit 108 (FIG. 1) such that, as described in further detailbelow, each sensor 126 can send electrical signals to and receiveelectrical signals from the catheter interface unit 108 during use.

In general, the sensors 126 can be positioned along one or both of theinner portion 136 and the outer portion 138 of the ablation electrode124. For example, the sensors 126 can extend through a portion of theablation electrode 124. Such positioning of the sensors 126 through aportion of the ablation electrode 124 can facilitate forming a robustmechanical connection between the sensors 126 and the ablation electrode124. Additionally, or alternatively, positioning the sensors 126 througha portion of the ablation electrode 124 can facilitate measuringconditions along the outer portion 138 and the inner portion 136 of theablation electrode 124.

The sensors 126 can be substantially uniformly spaced from one another(e.g., in a circumferential direction and/or in an axial direction)along the deformable portion 142 of the ablation electrode 124 when thedeformable portion 142 of the ablation electrode 124 is in anuncompressed state. Such substantially uniform distribution of thesensors 126 can, for example, facilitate determining an accuratedeformation and/or temperature profile of the deformable portion 142during use.

Each sensor 126 can act as an electrode (e.g., a surface electrode) todetect electrical activity of the heart in an area local to the sensor126 and, further or instead, each sensor 126 can include a flexibleprinted circuit 150, a thermistor 152 secured between portions of theflexible printed circuit 150, and a termination pad 155 opposite thethermistor 152. As an example, the sensor 126 can be mounted on thedeformable portion 142 of the ablation electrode 124 with the thermistor152 disposed along the outer portion 138 of the deformable portion 142and the termination pad 155 disposed along the inner portion 136 of thedeformable portion 142. In certain instances, the thermistor 152 can bedisposed along the outer portion 138 to provide an accurate indicationof tissue temperature. A thermally conductive adhesive or otherconductive material can be disposed over the thermistor 152 to securethe thermistor 152 to the flexible printed circuit 150.

In some implementations, each sensor 126 can include a radiopaqueportion and/or a radiopaque marker. The addition of radiopacity to thesensor 126 can, for example, facilitate visualization (e.g., usingfluoroscopy) of the sensor 126 during use. Examples of radiopaquematerial that can be added to the sensor 126 include: platinum, platinumiridium, gold, radiopaque ink, and combinations thereof. The radiopaquematerial can be added in any pattern that may facilitate visualizationof the radiopaque material such as, for example, a dot and/or a ring.

In certain implementations, each sensor 126 can form part of anelectrode pair useful for detecting contact between each sensor 126 andtissue. For example, electric energy (e.g., current) can be driventhrough each sensor 126 and another electrode (e.g., any one or more ofthe various different electrodes described herein) and a change in ameasured signal (e.g., voltage or impedance) can be indicative of thepresence of tissue. Because the position of the ablation electrode 124is known, the detection of contact through respective measured signalsat the sensors 126 can be useful for determining a shape of the anatomicstructure in which the ablation electrode 124 is disposed during thecourse of a medical procedure.

In use, each sensor 126 can, further or instead, act as an electrode todetect electrical activity in an area of the heart local to therespective sensor 126, with the detected electrical activity forming abasis for an electrogram associated with the respective sensor 126 and,further or instead, can provide lesion feedback. The sensors 126 can bearranged such that electrical activity detected by each sensor 126 canform the basis of unipolar electrograms and/or bipolar electrograms.Additionally, or alternatively, the sensors 126 can cooperate with acenter electrode (e.g., an electrode associated with an irrigationelement, such as a center electrode 235 in FIGS. 21 and 22, or theirrigation element itself, such as the irrigation element 128 in FIG. 3)to provide near-unipolar electrograms, as described in greater detailbelow. It should be appreciated that the sensors 126 and a centerelectrode can cooperate to provide near-unipolar electrograms inaddition, or as an alternative, to any one or more of the variousdifferent methods of determining contact, shape, force, and impedancedescribed herein, each of which may include further or alternativecooperation between the sensors 126 and a center electrode.

FIGS. 12A-12C are a schematic representation of an exemplary method ofmaking the ablation electrode 124 from a sheet 156 of material.

As shown in FIG. 12A, the sheet 156 of material is flat. As used herein,a flat material includes a material exhibiting flatness within normalmanufacturing tolerances associated with the material. The material ofthe sheet 156 is conductive and, optionally, also radiopaque. Forexample, the sheet 156 can be nitinol.

The thickness of the sheet 156 can correspond to the thickness of theablation electrode 124. For example, the thickness of the sheet 156 canbe greater than about 0.1 mm and less than about 0.20 mm. In certainimplementations, however, the thickness of the sheet 156 can be largerthan at least a portion of the thickness of the ablation electrode 124such that the removal of material from the flat sheet includes removalof material in a thickness direction of the sheet 156. For example,material can be selectively removed in the thickness direction of thesheet 156 to produce the ablation electrode 124 with a variablethickness (e.g., the ablation electrode 124 can be thinner along thejoints 141 a (FIGS. 6-8) to facilitate flexing).

As shown in FIG. 12B, material can be removed from the sheet 156 todefine the open area of the deformable portion 142 and to define thecoupling portion 140. In particular, the removal of material along thedeformable portion 142 can define the struts 144 b and the joints 141 a.

The material of the sheet 156 can be removed, for example, by using anyof various different subtractive manufacturing processes. As an example,the material of the sheet 156 can be removed using chemical etching(also known as photo etching or photochemical etching) according to anyone or more methods that are well known in the art and generally includeremoving material by selectively exposing the material to an acid toremove the material. Additionally, or alternatively, the material of thesheet 156 can be removed by laser cutting the material. The removal ofmaterial can be done to create openings in the sheet 156 and/or to thinselected portions of the sheet 156.

Because the sheet 156 is flat, removing material from the sheet 156 toform the deformable portion 142 can have certain advantages. Forexample, as compared to removing material from a curved workpiece,removing material from the sheet 156 can facilitate controllinggeometric tolerances. Additionally, or alternatively, as compared toremoving material from a curved workpiece, removing material from thesheet 156 can facilitate placement of sensors (e.g., while the sheet 156is flat). In certain implementations, as compared to removing materialfrom a curved workpiece, removing material from the sheet 156 canreduce, or even eliminate, the need to shape set the sheet 156, as thedistal and proximal sections can be put together to form the shape ofthe ablation electrode 124 (e.g., a substantially spherical shape).

In certain implementations, the material removed from the sheet 156 candefine eyelets 157 disposed at one end of at least a portion of thestruts 144 b. The eyelets 157 can be, for example, defined at theintersection of two or more of the struts 144 b.

In general, the material forming the ablation electrode 124 can beprocessed at any of various different stages of fabrication of theablation electrode 124. For example, with the material removed from thesheet to define the struts 144 a, 144 b and the joints 141 a as shown inFIG. 12B, one or more surfaces of the material can be electropolished.Such electropolishing can, for example, be useful for smoothing surfacesand/or otherwise producing fine adjustments in the amount of materialalong the ablation electrode 124.

As shown in FIG. 12C, with the material removed from the sheet 156 todefine the struts 144 a, 144 b and the joints 141 a, the sections 158are bent into proximity with one another and joined to one another toform a unitary three-dimensional structure having the overall shape ofthe ablation electrode 124. For example, the struts 144 b can be benttoward one another and the fastener 141 b can couple the portion of thestruts 144 b to one another at the eyelets 157, thus defining a closeddistal end of the deformable portion 142 of the ablation electrode 124.With the deformable portion 142 defined, the fastener 141 b can be at adistalmost portion of the deformable portion 142.

In certain implementations, the fastener 141 b can be a rivet. In suchimplementations, the eyelets 157 can be, for example, aligned with oneanother such that the fastener 141 b passes through the aligned eyelets157 to hold them together through force exerted on the eyelets 157 bythe fastener 141 b. Additionally, or alternatively, a secondaryoperation such as welding can secure the fastener 141 b to the struts144 b at the eyelets 157.

Referring now to FIGS. 13A-E, to perform a cardiac ablation treatment,the distal end portion 132 of the catheter shaft 122 and, thus, theablation electrode 124 can be first introduced into the patient,typically via a femoral vein or artery. FIGS. 13A-E schematicallyillustrate a series of steps carried out to introduce the ablationelectrode 124 into the patient.

In a first step, shown in FIG. 13A, an introducer sheath 162 ispositioned within a blood vessel of the patient (e.g., the femoralartery of the patient) and the ablation electrode 124 is positioned forinsertion into the introducer sheath 162.

In a second step, shown in FIG. 13B, the user grasps the handle 120 ofthe catheter 104 and distally advances an insertion sheath 164 along thecatheter shaft 122 until the insertion sheath 164 surrounds the ablationelectrode 124. As the insertion sheath 164 is advanced over the ablationelectrode 124, the ablation electrode 124 collapses to a diametercapable of being inserted into the introducer sheath 162.

In a third step, shown in FIG. 13C, the user inserts the insertionsheath 164 (containing the ablation electrode 124) into the introducersheath 162 and distally advances the catheter 104.

In a fourth step, shown in FIG. 13D, after positioning the ablationelectrode 124 within the introducer sheath 162, the ablation electrode124 is advanced out of the insertion sheath 164 that is then leftsurrounding the proximal end portion 130 of the catheter shaft 122throughout the remainder of the treatment.

In a fifth step, shown in FIG. 13E, the catheter 104 is advanced throughthe introducer sheath 162 and the patient's vasculature until theablation electrode 124 reaches the treatment site in the heart of thepatient. As the ablation electrode 124 is extended distally beyond theintroducer sheath 162, the ablation electrode 124 can expand to theuncompressed state.

Because the ablation electrode 124 is collapsible, the introducer sheath162 can have a small diameter that can be inserted through acorrespondingly small insertion site. In general, small insertion sitesare desirable for reducing the likelihood of infection and/or reducingthe amount of time required for healing. In certain implementations, theintroducer sheath 162 can have an 8 French diameter, and the deformableportion 142 (FIG. 3) of the ablation electrode 124 can be collapsible toa size deliverable through the introducer sheath 162 of this size. Insome implementations, the irrigation element 128 is additionallycollapsible to a size smaller than the size of the ablation electrode124 such that the irrigation element 128 and the ablation electrode 124are, together, deliverable through the introducer sheath 162 of thissize.

FIGS. 14A-C schematically represent an exemplary method of positioningthe deformable portion 142 of the ablation electrode 124 into contactwith tissue “T” at the treatment site. It should be appreciated that,because the delivery of ablation energy to the tissue “T” at thetreatment site is enhanced by contact between the ablation electrode 124and the tissue “T,” such contact is established prior to delivery ofablation energy.

In a first step, shown in FIG. 14A, the deformable portion 142 of theablation electrode 124 is away from the tissue “T” and, thus, in anuncompressed state. In certain instances, this uncompressed state isobservable through fluoroscopy. That is, the shape of the deformableportion 142 can be observed in the uncompressed state.

In a second step, shown in FIG. 14B, the deformable portion 142 of theablation electrode 124 makes initial contact with the tissue “T.”Depending on the nature of the contact between the tissue “T” and thedeformable portion 142 of the ablation electrode 124, deformation of thedeformable portion 142 may or may not be observable through fluoroscopyalone. For example, the contact force on the deformable portion 142 maybe insufficient to compress the deformable portion 142 to an extentobservable using fluoroscopy. Additionally, or alternatively, thecontact may not be observable, or may be difficult to observe, in thedirection of observation provided by fluoroscopy.

In a third step, shown in FIG. 14C, the deformable portion 142 of theablation electrode 124 is moved further into contact with the tissue “T”such that sufficient contact is established between the deformableportion 142 and the tissue “T” to deform the deformable portion 142.While such deformation may be observable using fluoroscopy, the degreeand/or direction of the deformation is not readily determined usingfluoroscopy alone. Further, as is also the case with initial contact,the contact and/or degree of contact may not be observable, or may bedifficult to observe, in the direction of observation provided byfluoroscopy. Accordingly, as described in greater detail below,determining apposition of the deformable portion 142 to the tissue “T”can, additionally or alternatively, include sensing the position of thedeformable portion 142 based on signals received from the sensors 126.

Referring again to FIGS. 1 and 3, the sensors 126 can be used todetermine the shape of the deformable portion 142 of the ablationelectrode 124 and, thus, determine whether and to what extent certainregions of the deformable portion 142 are in contact with the tissue“T.” It should be appreciated, however, that the sensing methodsdescribed herein can be carried out using the sensors 126, alone or incombination with another electrode, such as an electrode carried on anirrigation element, as described in greater detail below.

For example, the processing unit 109 a can control the generator 116and/or another electrical power source to drive an electrical signalbetween any number and combination of electrode pairs formed by anycombination of electrodes associated with the ablation electrode 124,and the processing unit 109 a can receive a signal (e.g., a signalindicative of voltage) from another electrode pair or the same electrodepair. For example, the processing unit 109 a can control the generator116 to drive one or more of the sensors 126, the ablation electrode 124,the irrigation element 128, and a center electrode (e.g., a centerelectrode 235 shown in FIGS. 21 and 22). Additionally, or alternatively,multiple pairs can be driven in a multiplexed manner using timedivision, frequency division, code division, or combinations thereof.The processing unit 109 a can also, or instead, receive one or moremeasured electrical signals from one or more of the sensors 126, theablation electrode 124, the irrigation element 128, and a centerelectrode (e.g., the center electrode 235 shown in FIGS. 21 and 22). Thedriven electrical signal can be any of various, different forms,including, for example, a prescribed current or a prescribed voltage. Incertain implementations, the driven electrical signal is an 8 kHzalternating current applied between one of the sensors 126 and theirrigation element 128.

In an exemplary method, the impedance detected by an electrode pair canbe detected (e.g., as a signal received by the processing unit 109 a)when an electrical signal is driven through the electrode pair. Theimpedance detected for various electrode pairs can be compared to oneanother and relative distances between the members of each electrodepair determined. For example, if the sensors 126 are identical, eachsensor 126 can be driven as part of a respective electrode pairincluding the irrigation element 128. For each such electrode pair, themeasured impedance between the electrode pair can be indicative ofrelative distance between the particular sensor 126 and the irrigationelement 128 forming the respective electrode pair. In implementations inwhich the irrigation element 128 is stationary while electrical signalsare driven through the electrode pairs, the relative distance betweeneach sensor 126 and the irrigation element 128 can be further indicativeof relative distance between each sensor 126 and each of the othersensors 126. In general, driven electrode pairs with lower measuredimpedance are closer to one another than those driven electrode pairswith higher measured impedance. In certain instances, electrodesassociated with the ablation electrode 124 (e.g., one or more of thesensors 126) that are not being driven can be measured to determineadditional information regarding the position of the driven currentpair.

The measurements received by the processing unit 109 a and associatedwith the driven current pairs alone, or in combination with themeasurements at the sensors 126 that are not being driven, can be fit toa model and/or compared to a look-up table to determine displacement ofthe deformable portion 142 of the ablation electrode 124. For example,the determined displacement of the deformable portion 142 of theablation electrode 124 can include displacement in at least one of anaxial direction or a lateral (radial) direction. It should beappreciated that, because of the spatial separation of the current pairsin three dimensions, the determined displacement of the deformableportion 142 of the ablation electrode 124 can be in more than onedirection (e.g., an axial direction, a lateral direction, andcombinations thereof). Additionally, or alternatively, the determineddisplacement of the deformable portion 142 of the ablation electrode 124can correspond to a three-dimensional shape of the deformable portion142 of the ablation electrode 124.

Based on the determined displacement of the deformable portion 142 ofthe ablation electrode 124, the processing unit 109 a can send anindication of the shape of the deformable portion 142 of the ablationelectrode 124 to the graphical user interface 110. Such an indication ofthe shape of the deformable portion 142 can include, for example, agraphical representation of the shape of the deformable portion 142corresponding to the determined deformation.

In implementations in which the force-displacement response of thedeformable portion 142 is reproducible (e.g., as shown in FIG. 9), theprocessing unit 109 a can determine force applied to the deformableportion 142 based on the determined displacement of the deformableportion 142. For example, using a lookup table, a curve fit, or otherpredetermined relationship, the processing unit 109 a can determine thedirection and magnitude of force applied to the deformable portion 142based on the magnitude and direction of the displacement of thedeformable portion 142, as determined according to any one or more ofthe methods of determining displacement described herein. It should beappreciated, therefore, that the reproducible relationship between forceand displacement along the deformable portion 142, coupled with theability to determine displacement using the sensors 126 disposed alongthe deformable portion 142, can facilitate determining whether anappropriate amount of force is being applied during an ablationtreatment and, additionally or alternatively, can facilitate determiningappropriate energy and cooling dosing for lesion formation.

FIGS. 15A-B schematically represent an exemplary method of cooling theablation electrode 124 at the treatment site with irrigation fluid fromthe irrigation element 128. For the sake of clarity of illustration, asingle jet of irrigation fluid is shown. It should be appreciated,however, that a plurality of jets issue from the irrigation element 128during use. In certain implementations, the irrigation fluid issubstantially uniformly directed to the inner portion 136 of theablation electrode 124. Additionally, or alternatively, a portion of theirrigation fluid can be directed in a direction distal to the irrigationelement 128 and a portion of the irrigation fluid can be directed in adirection proximal to the irrigation element 128.

In a first step, shown in FIG. 15A, the ablation electrode 124 ispositioned at the treatment site with the outer portion 138 disposedtoward tissue. A baseline flow of irrigation fluid is delivered to theirrigation element 128 prior to delivery of ablation energy to theablation electrode 124. The baseline flow of irrigation fluid can be,for example, about 0.5 psi above the patient's blood pressure to reducethe likelihood that blood will enter the irrigation element 128 andclot. Further, as compared to always delivering irrigation fluid at ahigher pressure, the delivery of this lower pressure of irrigation fluidwhen ablation energy is not being delivered to the ablation electrode124 can reduce the amount of irrigation fluid delivered to the patientduring treatment.

In a second step, shown in FIG. 15B, ablation energy is directed to atleast some of the outer portion 138 of the ablation electrode 124 incontact with the tissue “T”. As the ablation energy is delivered to theablation electrode 124, the pressure of the irrigation fluid can beincreased, resulting in a higher pressure flow directed from theirrigation element 128 toward the inner portion 136 of the ablationelectrode 124. The higher flow of irrigation fluid at the inner portion136 can result in turbulent flow which, compared to laminar flow, canimprove heat transfer away from the ablation electrode 124. For example,each jet of irrigation fluid issuing from the irrigation element 128 canhave a Reynolds number above about 2000 (e.g., greater than about 2300)at the inner portion 136 of the ablation electrode 124 when thedeformable portion 142 is in the uncompressed state.

While certain embodiments have been described, other embodiments areadditionally or alternatively possible.

For example, while forming the deformable portion of an ablationelectrode has been described as including removal of material from aflat sheet, other methods of forming a deformable portion of an ablationelectrode are additionally or alternatively possible. For example, adeformable portion of an ablation electrode can be formed by removingmaterial (e.g., by laser cutting) from a tube of material (e.g., a tubeof nitinol). With the material removed, the tube can be bent into asubstantially enclosed shape such as the substantially spherical shapesdescribed herein.

As another example, while the deformable portion of an ablationelectrode has been described as being formed by removing material from aunitary structure of material (e.g., from a plate and/or from a tube),other methods of forming a deformable portion of an ablation electrodeare additionally or alternatively possible. For example, a deformableportion of an ablation electrode can include a mesh and/or a braid. Themesh material can be, for example, nitinol. It should be appreciatedthat this mesh and/or braided portion of the ablation electrode can movebetween a compressed and uncompressed state.

As yet another example, while an ablation electrode has been describedas having a deformable portion, along which sensors are disposed fordetermining displacement of the deformable portion, other configurationsfor determining displacement are additionally or alternatively possible.For example, a plurality of coils can be disposed along a deformableportion of an ablation electrode. In use, some coils in the pluralitycan be used to emit a magnetic field while other coils in the pluralitycan be used to measure the resultant magnetic field. The signalsmeasured can be used to determine displacement of the deformableportion. This determined displacement of the deformable portion can beused, for example, to determine the shape of the deformable portion and,additionally or instead, to determine the force applied to thedeformable portion according to any one or more of the methods describedherein. Further, or instead, a plurality of ultrasound transducers orother types of image sensors can be disposed along a deformable portionof an ablation electrode, on an irrigation element enveloped by thedeformable portion, or a combination thereof. The signals measured bythe ultrasound transducers or other types of image sensors can be usedto determine displacement of the deformable portion.

As still another example, while the deformable portion of an ablationelectrode has been described as being self-expandable from thecompressed state to the uncompressed state, the deformable portion ofthe ablation electrode can be additionally or alternatively expandedand/or contracted through the application of external force. Forexample, a catheter such as any one or more of the catheters describedherein can include a sliding member extending from the handle, though acatheter shaft, and to an ablation electrode. The sliding member can becoupled (e.g., mechanically coupled) to the ablation electrode such thataxial movement of the sliding member relative to the catheter shaft canexert compression and/or expansion force on the deformable portion ofthe ablation electrode. For example, distal movement of the slidingmember can push the ablation electrode in a distal direction relative tothe catheter shaft such that the deformable portion of the ablationelectrode collapses to a compressed state (e.g., for retraction,delivery, or both). In addition, or as an alternative, proximal movementof the sliding member can pull the ablation electrode in a proximaldirection relative to the catheter shaft such that the deformableportion of the ablation electrode expands to an uncompressed state(e.g., for the delivery of treatment). In certain implementations, thesliding member can be mechanically coupled to a portion of the handlesuch that movement of the sliding member can be controlled at thehandle. It should be appreciated that the sliding member can be anelongate member (e.g., a wire) that is sufficiently flexible to bendwith movement of the shaft while being sufficiently rigid to resistbuckling or other types of deformation in response to the force requiredto move the deformable portion of the ablation electrode.

As yet another example, while the irrigation element has been describedas including a substantially rigid stem and bulb configuration, otherconfigurations of the irrigation element are additionally oralternatively possible. For example, referring now to FIG. 16, anirrigation element 128 a can include an axial portion 166 and a helicalportion 168. The irrigation element 128 a can be used in any one or moreof the catheters described herein. For example, the irrigation element128 a can be used in addition to or instead of the irrigation element128, as described with respect to FIGS. 3-5.

The axial portion 166 and the helical portion 168 are in fluidcommunication with one another and, in certain implementations, with anirrigation lumen defined by the catheter shaft. At least the helicalportion 168 and, optionally, the axial portion 166 define a plurality ofirrigation holes 134 a along at least a portion of the length of theirrigation element 128 a. In use, the delivery of irrigation fluidthrough the irrigation holes 134 a can result in an axially,circumferentially, and/or radially distributed pattern. Unless otherwiseindicated or made clear from the context, the irrigation element 128 acan be used in addition to or instead of the irrigation element 128(FIG. 3). Thus, for example, it should be understood that the irrigationelement 128 a can provide substantially uniform cooling along the innerportion 136 of the ablation electrode 124 (FIG. 3).

The irrigation holes 134 a can be similar to the irrigation holes 134defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 a can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 a can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

The axial portion 166 of the irrigation element 128 can be coupled to acatheter shaft (e.g., to a distal end portion of the catheter shaft suchas the distal end portion 132 of the catheter shaft 122 described withrespect to FIGS. 2-4). Additionally, or alternatively, the axial portion166 can extend distally from the catheter shaft. For example, the axialportion 166 can extend distally from the catheter shaft, along an axisdefined by the irrigation lumen.

In general, the helical portion 168 extends in a radial direction awayfrom the axial portion 166. In certain implementations, a maximum radialdimension of the helical portion 168 is less than an outer diameter ofthe catheter shaft. In such implementations, the helical portion 168 canremain in the same orientation during delivery and use of the catheter(e.g., during any of the delivery and/or use methods described herein).In some implementations, however, the helical portion 168 can beresiliently flexible (e.g., a nitinol tube shape set in a helicalconfiguration) such that the maximum radial extent of the helicalportion 168 is less than an outer diameter of the catheter shaft duringdelivery to the treatment site and expands such that the maximum radialextent of the helical portion 168 is greater than the outer diameter ofthe catheter shaft in a deployed position. It should be appreciatedthat, in the deployed position, the helical portion can be positionedcloser to the inner surface of an ablation electrode, which canfacilitate delivery of irrigation fluid to the inner surface of theablation electrode.

In addition to extending in a radial direction away from the cathetershaft, the helical portion 168 extends in a circumferential directionrelative to the axial portion 166. For example, the helical portion 168can extend circumferentially about the axial portion 166 through atleast one revolution. Such circumferential extension of the helicalportion through at least one revolution can facilitate substantiallyuniform dispersion of irrigation fluid about an inner surface of asubstantially spherical ablation electrode enveloping the helicalportion 168.

Optionally, the helical portion 168 can further extend in an axialdirection relative to the axial portion 166. Thus, as used herein, thehelical portion 168 should be understood, in the most general sense, toinclude any of various different helical patterns that are substantiallyplanar and/or various different helical patterns that extend axiallyrelative to the axial portion 166.

As another example, while the irrigation element has been described ashaving a discrete number of uniform irrigation holes, otherimplementations are additionally or alternatively possible. For example,referring now to FIG. 17, an irrigation element 128 b can be a porousmembrane defining a plurality of openings 170. In general, the pluralityof openings 170 are a property of the material forming the irrigationelement 128 c and are, therefore, distributed (e.g., non-uniformlydistributed and/or uniformly distributed) along the entire surface ofthe irrigation element 128 b. Because the openings 170 are a property ofthe material forming the irrigation element 128 b, the plurality ofopenings 170 can be substantially smaller than irrigation holes formedin an irrigation element through laser drilling or other similarsecondary processes. Unless otherwise indicated or made clear from thecontext, the irrigation element 128 b can be used in addition to orinstead of the irrigation element 128 (FIG. 3) and/or the irrigationelement 128 a (FIG. 16). Thus, for example, it should be understood thatthe irrigation element 128 b can provide substantially uniform coolingalong the inner portion 136 of the ablation electrode 124 (FIG. 3).

In certain implementations, the irrigation element 128 b can include anarrangement of one or more polymers. Such an arrangement can be porousand/or microporous and, as an example, can be formed ofpolytetrafluoroethylene (PTFE). In such implementations, the openings170 can be defined by spaces between polymeric fibers or through thepolymeric fibers themselves and are generally distributed along theentire surface of the irrigation element 128 b. It should be appreciatedthat the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan produce a substantially uniform spray of irrigation fluid. Further,the large number of the openings 170 and the distribution of theopenings 170 along the entire surface of the irrigation element 128 bcan facilitate interaction of multiple different fluid jets and, thus,the development of turbulent flow of irrigation fluid.

The size and distribution of the openings 170 defined between or throughpolymeric fibers can allow the irrigation element 128 b to act as aselective filter. For example, because blood molecules are substantiallylarger than water molecules, the size (e.g., the average size) of theopenings 170 can be smaller than blood molecules but larger than watermolecules. It should be appreciated that such sizing of the openings 170can permit egress of irrigation fluid from the irrigation element 128 bwhile preventing ingress and, thus, clotting of blood molecules into theirrigation element 128 b.

The arrangement of one or more polymers of the irrigation element 128 bcan include electrospun polytetrafluorethylene and/or expandedpolytetrafluoroethylene (ePTFE). In certain implementations, thearrangement of one or more polymers is nonwoven (as shown in FIG. 17)resulting in the spacing between the fibers being substantiallynon-uniform such that the openings 170 defined by the spacing betweenthe fibers are of non-uniform size and/or non-uniform distribution. Insome implementations, the irrigation element 128 b can include a wovenor fabric arrangement of polymers through which irrigation fluid can bedirected. For example, the fabric can be formed of one or more polymersor other biocompatible materials woven together to form a substantiallyuniform porous barrier through which, in use, irrigation fluid may pass.Examples of polymers that can be arranged together into a fabricsuitable for forming the irrigation element 128 c include, but are notlimited to, one or more of the following: polyester, polypropylene,nylon, PTFE, and ePTFE.

In some implementations, the irrigation element 128 b can include anopen cell foam such that the openings 170 are defined by cells of theopen cell foam along the surface of the irrigation element 128 b. Insuch implementations, irrigation fluid can move through tortuous pathsdefined by the open cell foam until the irrigation fluid reaches theopenings 170 along the surface of the irrigation element 128 b, wherethe irrigation fluid exits the irrigation element 128 b. It should beappreciated that, in such implementations, the openings 170 aredistributed along the entire surface of the irrigation element 128 b,resulting in spray of irrigation fluid issuing from the irrigationelement 128 b in a substantially uniform and substantially turbulentpattern.

As yet another example, while irrigation elements have been described asincluding a resilient, expandable helical portion, other types ofresilient, expandable irrigation elements are additionally oralternatively possible. For example, referring now to FIG. 18, anirrigation element 128 c can be a resilient, inflatable structure, suchas balloon, disposed along a distal end portion 132′ of a catheter shaft122′ and in fluid communication with a lumen 151′. In certainimplementations, the irrigation element 128 c and the ablation electrode124′ can each be coupled to the distal end portion 132′ of the cathetershaft 122′. Unless otherwise indicated or made clear from the context,an element designated with a primed (′) element number in FIG. 18 issimilar to a corresponding element designated with an unprimed number inother figures of the present disclosure and, thus, should be understoodto include the features of the corresponding element designated with anunprimed number. As one example, therefore, the ablation electrode 124′should be understood to correspond to the ablation electrode 124 (FIG.3), unless otherwise specified.

In certain implementations, the irrigation element 128 c is expandable.For example, the irrigation element 128 c can be uninflated and/orunderinflated in a delivery state of the distal end portion 132′ of thecatheter shaft 122′ to a treatment site according to any of the methodsdescribed herein. In such a delivery state, the irrigation element 128 ccan be delivered to the treatment site with a low profile (e.g., aprofile that is less than or equal to a maximum outer dimension of thecatheter shaft 122′). At the treatment site, the irrigation element 128c can be inflated to expand from the delivery state to an expandedstate. For example, the irrigation element 128 c can expand in a radialdirection beyond an outermost dimension of the catheter shaft 122′.

The irrigation element 128 c can be a non-compliant balloon or asemi-compliant balloon. In such implementations, the irrigation element128 c can be substantially resistant to deformation when in an inflatedstate. Thus, in instances in which the irrigation element 128 c isnon-compliant or semi-compliant, the irrigation element 128 c can resistdeformation when contacted by an inner portion 136′ of the deformableportion 142′ of the ablation electrode 124′. As compared to a compliantballoon, this resistance to deformation by the irrigation element 128 ccan facilitate, for example, control over the flow of irrigation fluidthrough the irrigation element 128 c.

In some implementations, the irrigation element 128 c is a balloonformed of one or more polymers. Polymers can be, for example,sufficiently flexible to expand from the delivery state to the expandedstate while withstanding forces created by the movement of irrigationfluid through the irrigation element 128 c. In instances in which theirrigation element 128 c is formed of one or more polymers, irrigationholes can be formed in polymers through laser drilling or other similarsecondary processes. Examples of polymers that can be used to form theirrigation element 128 c include one or more of: thermoplasticpolyurethane, silicone, poly(ethylene terephthalate), and polyetherblock amide.

The irrigation element 128 c can define a plurality of irrigation holes134 c. The irrigation holes 134 c can be similar to the irrigation holes134 defined by the irrigation element 128 (FIG. 3). For example, theirrigation holes 134 c can be the same size and shape as the irrigationholes 134 defined by the irrigation element 128. Additionally, oralternatively, the irrigation holes 134 c can have the same open area asthe irrigation holes 134 defined by the irrigation element 128.

In use, irrigation fluid can flow from the lumen 151′, into theirrigation element 128 c, and can exit the irrigation element 128 cthrough the plurality of irrigation holes 134 c. In general, theplurality of irrigation holes 134 c can have a combined area that isless than the cross-sectional area of the lumen 151′ such that fluidpressure can build in the inflatable element 128 c as the irrigationfluid moves through the irrigation element 128 c. It should beappreciated, then, that the pressure in the inflatable element 128 c,resulting from the flow of irrigation fluid through the irrigationelement 128 c, can inflate the irrigation element 128 c (e.g., from thedelivery state to the expanded state).

In certain implementations, the volume defined by an inner portion 136′of the ablation electrode 124′ in an expanded or uncompressed state islarger than the volume defined by the irrigation element 128 c in anexpanded state. Thus, for example, the inner portion 136′ of theablation electrode 124′ (e.g., along the deformable portion 142′) can bespatially separated from at least a portion of the surface area of theirrigation element 128 c when the irrigation element 128 c is in theexpanded state. This spatial separation can be advantageous, forexample, for developing turbulence of irrigation fluid issuing from theirrigation holes 134 c prior to reaching the inner portion 136′ of theablation electrode 124′. It should be appreciated that, as compared toless turbulent flow and/or laminar flow, such turbulence of the flow ofirrigation fluid at the inner portion 136′ of the ablation electrode124′ can facilitate efficient cooling of the ablation electrode 124′.

The irrigation element 128 c can be enveloped by the ablation electrode124′ in an uncompressed state to facilitate, for example, coolingsubstantially the entire inner portion 136′ of the ablation electrode124′. Additionally, or alternatively, enveloping the irrigation element128 c with the ablation electrode 124′ can reduce the likelihood ofexposing the irrigation element 128 c to undesirable forces such as, forexample, forces that can be encountered as the ablation electrode 124′and the irrigation element 128 c are moved to the treatment site.

In the expanded state, the irrigation element 128 c can include asubstantially ellipsoidal portion. As used herein, a substantiallyellipsoidal portion can include a substantially spherical shape anddeformations of a substantially spherical shape.

In certain implementations, the irrigation holes 134 c are defined onthis ellipsoidal portion of the irrigation element 128 c. Thus, in suchimplementations, the ellipsoidal portion of the irrigation element 128 ccan facilitate directing irrigation fluid in multiple, different axialand radial directions. For example, the irrigation holes 134 c can bespaced circumferentially (e.g., about the entire circumference) aboutthe ellipsoidal portion of the irrigation element 128 c such thatirrigation fluid can be directed toward the inner portion 136′ of theablation electrode 142′ along various different radial directions. As anadditional or alternative example, the irrigation holes 134 c can bespaced axially (e.g., along an entire axial dimension of the ellipsoidalportion of the irrigation element 128 c) such that the irrigation fluidcan be directed toward the inner portion 136′ of the ablation electrode142′ along proximal and/or distal axial directions.

A plurality of sensors 126′ can be supported on the deformable portion142′ of the ablation electrode 124′. In use, the plurality of sensors126′ can be used to detect deformation of the deformable portion 142′.For example, the irrigation element 128 c can include a sensor 172 andelectrical signals can be driven between the one or more electrodes onthe irrigation element 128 c and each of the plurality of sensors 126′according to any of the methods described herein.

While the plurality of sensors 126′ can be used in cooperation with thesensor 172 on the irrigation element 128 c, other configurations forsensing deformation of the deformable portion 142′ are also or insteadpossible. For example, referring now to FIGS. 19 and 20, a plurality ofsensors 174 can be supported along an ablation electrode 124″ at leastpartially enveloping an irrigation element 128 c″. Unless otherwiseindicated or made clear from the context, an element designated with adouble primed (″) element number in FIGS. 19 and 20 is similar to acorresponding element designated with an unprimed number and/or with aprimed number in other figures of the present disclosure and, thus,should be understood to include the features of the correspondingelement designated with an unprimed number and/or with a primed number.As one example, the irrigation element 128 c″ should be understood toinclude the features of the irrigation element 128 c (FIG. 18), unlessotherwise specified or made clear from the context. As another example,the ablation electrode 124″ should be understood to include the featuresof the ablation electrode 124 (FIGS. 3 and 4) and/or of the ablationelectrode 124′ (FIG. 18), unless otherwise specified or made clear fromthe context.

Each sensor 174 can include a flexible printed circuit and/or athermistor similar to any of the flexible printed circuits and/orthermistors described herein, including the flexible printed circuit 150and/or thermistor 152 described above with respect to FIGS. 10 and 11.

In the uncompressed state of the ablation electrode 124″, the innerportion 136″ of the ablation electrode 124″ is spatially separated froma least a portion of a surface of the irrigation element 128 c″ suchthat, for example, at least one of the plurality of sensors 174 is notin contact with the irrigation element 128 c″. In certainimplementations, the ablation electrode 124″ in the uncompressed stateis not in contact with any of the plurality of sensors 174. That is, insuch implementations in which the ablation electrode 124″, in theuncompressed state, is spatially separated from one or more of thesensors 126″, the default arrangement of the sensors 126″ is away fromthe irrigation element 128 c.

The ablation electrode 124″ can include a deformable portion 142″ thatis resiliently flexible from a compressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is in contact with theirrigation element 128 c″) to an uncompressed state (e.g., in which theinner portion 136″ of the ablation electrode 124″ is spatially separatedfrom at least a portion of the surface of the irrigation element 128c″). Thus, in such implementations, deformation of the deformableportion 142″ can place one or more of the plurality of sensors 174 intocontact with the irrigation element 128 c″ and sensing this contact canbe used to determine the shape of the deformable portion 142″ inresponse to a deformation force, such as a force exerted through contactwith tissue.

The sensors 174 can be axially and/or circumferentially spaced from oneanother along the deformable portion 142″ of the ablation electrode124″. For example, a first set of the sensors 174 can be disposed distalto a second set of the sensors 174 along the ablation electrode 124″(e.g., along the deformable portion 142″). It should be appreciated thatthe spatial resolution of the detected deformation of the deformableportion 142″ can be a function of the number and spatial distribution ofthe sensors 174, with a larger number of uniformly spaced sensors 174generally providing increased spatial resolution as compared to asmaller number of clustered sensors 174.

In use, an electrical signal can be driven between at least one of thesensors 174 and another one of the sensors 174. Measured electricalsignals generated between at least one of the sensors 174 and another ofthe sensors 174 can be received at a processing unit such as any of theprocessing units described herein (e.g., processing unit 109 a describedwith respect to FIG. 1).

Based at least in part on the measured electrical signals generatedbetween at least one of the sensors 174 and another of the sensors 174,deformation of the deformable portion 142″ of the ablation electrode124″ can be detected. For example, as the deformable portion 142″ of theablation electrode 124″ deforms, one or more of the sensors 174 can bebrought into contact with the irrigation element 128 c″. It should beappreciated that a certain amount of force is required to deform thedeformable portion 142″ by an amount sufficient to bring the one or moresensors 174 into contact with the irrigation element 128 c″. As usedherein, this force can be considered a threshold at least in the sensethat forces below this threshold are insufficient to bring the one ormore sensors 174 into contact with the irrigation element 128 c″ and,therefore, are not detected as contact between the one or more sensors174 and the irrigation element 128 c″.

Contact between the one or more sensors 174 and the irrigation element128 c″ can be detected, for example, as a change in the measuredelectrical signal received, by the processing unit, from the respectiveone or more sensors 174. As a non-limiting example, contact between oneor more of the sensors 174 and the irrigation element 128 c can bedetected as a rise in impedance of a respective one or more electricalsignals associated with the one or more sensors 174 in contact with theirrigation element 128 c.

The detection of deformation of the deformable portion 142″ of theablation electrode 124″ can, for example, include a determination ofwhether one or more of the sensors 174 is in contact with the irrigationelement 128 c. In addition, or instead, the detection of deformation ofthe deformable portion 142″ based on the measured electrical signals caninclude a detection of a degree and/or direction of deformation of thedeformable portion 142″. That is, a degree and/or direction ofdeformation of the deformable portion 142″ can be determined based onthe number and/or position of the one or more sensors 174 detected asbeing in contact with the irrigation element 128 c.

An indication of a determined state of the deformable portion 142″ canbe sent to a graphical user interface, such as any one or more of thegraphical user interfaces described herein (e.g., the graphical userinterface 110 described with respect to FIG. 1). In certainimplementations, the degree and/or orientation of deformation of thedeformable portion 142″ can be sent to the graphical user interface. Forexample, based on which sensors 174 are detected as being in contactwith the irrigation element 128 c, a corresponding representation of thecompressed state of the deformable portion 142″ can be sent to thegraphical user interface. The corresponding representation of thecompressed state of the deformable portion 142″ can be based on, forexample, a look-up table of shapes corresponding to differentcombinations of sensors 174 detected as being in contact with theirrigation element 128 c.

An exemplary method of making a catheter including the irrigationelement 128 c″ can include coupling (e.g., using an adhesive) theirrigation element 128 c″ to a distal end portion 132″ of a cathetershaft 122″. The deformable portion 142″ can be formed according to anyone or more of the methods described herein, and the deformable portion142″ can be positioned relative to the irrigation element 128 c″ suchthat the inner portion 136″ of the ablation electrode 124″ envelops theirrigation element 128 c″. The deformable portion 142″ can be coupled tothe catheter shaft 122″ relative to the irrigation element 128 c″ suchthat, in a compressed state, the inner portion 136″ of the ablationelectrode 124″ is in contact with the irrigation element 128 c″ and, inan uncompressed state, the inner portion 136″ of the ablation electrode124″ along the deformable portion 142″ is spatially separated from theirrigation element 128 c″.

As another example, while certain arrangements of struts to form cellsalong a deformable portion of an ablation electrode have been described,other configurations are additionally or alternatively possible. Forexample, referring now to FIGS. 21 and 22, a catheter 204 can include anablation electrode 224 having struts 244 b defining a plurality of cells247, with the struts 244 b progressively ganged together in a directionfrom a proximal region to a distal region of a deformable portion 242 ofthe ablation electrode 224. For the sake of efficient and cleardescription, elements designated by 200-series element numbers in FIGS.21 and 22 are analogous to or interchangeable with elements with100-series element numbers (including primed and double-primed elementnumbers) described herein, unless otherwise explicitly indicated or madeclear from the context, and, therefore, are not described separatelyfrom counterpart elements having 100-series element numbers, except tonote differences or to describe features that are more easily understoodwith reference to FIGS. 21 and 22. Thus, for example, catheter 204 inFIGS. 21 and 22 should generally be understood to be analogous to thecatheter 104 (FIGS. 1-4), unless otherwise explicitly indicated or madeclear from the context.

As used herein, a progressively ganged together configuration of thestruts 244 b can include an arrangement of the struts 244 b in which thenumber of cells in the plurality of cells 247 decreases in a givendirection. Thus, for example, the struts 244 b can be progressivelyganged together in the direction toward the distal end of the deformableportion 242 such that the number of cells 247 defined by the strutsdecreases in the direction toward the distal end of the deformableportion 242. Thus, as compared to a configuration in which struts areuniformly disposed about a shape, the closed end of the deformableportion 242 of the ablation electrode 224 can be formed by joiningtogether relatively few of the struts 244 b. This can be advantageouswith respect to, for example, achieving acceptable manufacturingtolerances or, further or instead, facilitating substantially uniformdistribution of current density along the deformable portion 242.

In some implementations, the cells in the plurality of cells 247 can bebounded by different numbers of struts 244 b, which can facilitateachieving a target distribution of current density along the deformableportion 242. For example, a first set of cells of the plurality of cells247 can be bounded by struts 244 b defining eyelets (e.g., eyelets 157in FIG. 12B), and a second set of cells of the plurality of cells 247can be bounded by fewer struts than the first set of cells. For example,the first set of cells of the plurality of cells 247 can be bounded byat least four struts 244 b.

In certain implementations, at least some of the cells 247 of theplurality of cells 247 are symmetric. Such symmetry can, for example,facilitate achieving substantially uniform current density in adeformable portion 242 of the ablation electrode 224. Additionally, oralternatively, such symmetry can be useful for achieving suitablecompressibility of the deformable portion for delivery to a treatmentsite (e.g., through a sheath) while also achieving suitable expansion ofthe deformable portion for use at the treatment site.

At least some of the cells 247 can have mirror symmetry. As used herein,a mirror symmetric shape includes a shape that is substantiallysymmetric about a plane intersecting the shape, with the substantialsymmetry allowing for the presence or absence of a sensor 226 on one orboth sides of the plane intersecting the shape. For example, at leastsome of the cells 247 can have mirror symmetry about a respective mirrorsymmetry plane passing through the respective cell 247 and containing acenter axis CL′-CL′ defined by a catheter shaft 222 and extending from aproximal end portion to a distal end portion of the catheter shaft 222.In the side view shown in FIG. 22, a mirror symmetry plane for some ofthe cells of the plurality of cells 247 is directed perpendicularly intothe page and passes through the center axis CL′-CL′. Additionally, oralternatively, it should be appreciated that the overall deformableportion 242 of the ablation electrode 224 can be symmetric about a planeincluding the center axis CL′-CL′, such as the plane directedperpendicularly into the page and passing through the center axisCL′-CL′.

The mirror symmetry of at least some of the cells of the plurality ofcells 247 and/or the overall deformable portion 242 can be useful, forexample, for uniform distribution of current density. Additionally, oralternatively, symmetry can facilitate expansion and contraction of thedeformable portion 242 of the ablation electrode 224 in a predictableand repeatable manner (e.g., with little to no plastic deformation). Forexample, each of the cells of the plurality of cells 247 can besymmetric about its respective symmetry plane in the compressed stateand in the uncompressed state of the deformable portion 242 of theablation electrode 224. With such symmetry in the compressed state andin the uncompressed state of the deformable portion 242, the deformableportion 242 can expand with little to no circumferential translation ofthe deformable portion 242 during expansion, which can facilitateaccurate knowledge of the position of the deformable portion 242 duringdelivery and deployment of the deformable portion 242.

The catheter 204 can be formed according to any one or more of thevarious different methods described herein. For example, the ablationelectrode 224 can be formed from a flat sheet or from a tube, asdescribed herein, such that the ablation electrode 224 has two openends. A fastener 241 b can be inserted through an end of at least someof the struts 244 b according to any of the various different methodsdescribed herein to couple ends of the struts 244 b to close one of thetwo open ends of the ablation electrode 224. An open end of ablationelectrode 224 (e.g., an end opposite the fastener 241 b) can be coupledto a distal end portion 232 of the catheter shaft 222 to form thecatheter 204.

The following simulation and experiment describe the uniformity ofcurrent density associated with the ablation electrode 224 in theuncompressed state. It is to be understood that the simulation andexperiment described below are set forth by way of example only, andnothing in the simulation or experiment shall be construed as alimitation on the overall scope of this disclosure.

Referring now to FIGS. 21-23, an irrigation element 228 can be envelopedby the deformable portion 242 of the ablation electrode 224 such thatthe deformable portion 242 forms an enclosure about the irrigationelement 228. The irrigation element 228 can be any of the variousdifferent irrigation elements described herein and can be in fluidcommunication with a catheter shaft 222. For example, the irrigationelement 228 can be disposed substantially along the center axis CL′-CL′,can extend distally from a distal end portion 232 of the catheter shaft222, and, also or instead, can define a plurality of irrigation holes234 disposed along the irrigation element 228 to direct irrigation fluidtoward the deformable portion 242 of the ablation electrode 224.Additionally, or alternatively, a center electrode 235 can be disposedalong the irrigation element 228 and directly or indirectly coupled tothe distal end portion 232 of the catheter shaft 222.

The irrigation element 228 can include a nozzle portion 229 disposedalong an end of a substantially cylindrical body 230. The plurality ofirrigation holes 234 can be defined along one or both of the nozzleportion 229 and the substantially cylindrical body 230. In general, theplurality of irrigation holes 234 can be sized and positioned to directfluid from the nozzle portion 229 in a variety of different spraypatterns. For example, the nozzle portion 229 can be substantiallyhemispherical to facilitate orienting at least some of the plurality ofirrigation holes 234 in multiple different directions. Additionally, oralternatively, at least some of the plurality of irrigation holes 234can be spaced axially, circumferentially, or both, about the cylindricalbody 230. In certain instances, the orientation of the plurality ofirrigation holes 234 along the nozzle portion 229, the cylindrical body230, or a combination thereof, can be useful for generatingsubstantially uniform distribution of irrigation fluid from theirrigation element 228 toward the ablation electrode 224. Additionally,or alternatively, the orientation of the plurality of irrigation holes234 in multiple different directions can be useful for creating aturbulent flow of the irrigation fluid, which can be useful forpromoting heat transfer away from the ablation electrode 224. Further inaddition, or in the alternative, the orientation of the plurality ofirrigation holes 234 in multiple different directions can be useful forentraining blood and increasing the volume velocity of fluid over theablation electrode 224 and tissue.

In the absence of force applied to the deformable portion 242 of theablation electrode 224, the center electrode 235 is spaced apart fromthe sensors 226. As the deformable portion 242 is brought into contactwith tissue through application of force applied to the deformableportion 242, it should be appreciated that, independent of orientationof the deformable portion 242 relative to tissue, the deformable portion242, and thus the sensors 226, makes initial contact with the tissuebefore the center electrode 235 makes initial contact with the tissue.In certain implementations, the center electrode 235 remains spaced fromtissue under normal operation. That is, the deformable portion 242 ofthe ablation electrode 224 can be sufficiently rigid to maintain spacingof the center electrode 235 from tissue under a normal range of contactforces, which are less than about 100 g (e.g., less than about 50 g).

In certain implementations, the irrigation element 228 can be one orboth of electrically and thermally isolated from the center electrode235. In such instances, the irrigation element 228 can be a groundedelectrode of the measurement circuit to reduce noise, measurement error,or both. For example, in instances in which the irrigation element 228is a grounded electrode, the irrigation element 228 can be connected toa ground node of the measurement circuit through a resistor (e.g., a 50kΩ resistor). As a further or alternative example, the irrigationelement 228 can be a driven electrode that is part of an analog feedbackcircuit, and electrical energy can be driven through the irrigationelement 228 such that a voltage measured on a reference electrode (e.g.,the center electrode 235) is reduced. In general, it should beappreciated that the use of the irrigation element 228 as a groundedelectrode or as a driven electrode, as the case may be, can reduce oreliminate the need to have a grounded or driven electrode carried on aseparate device (such as a right leg electrode). Such a reduction incomplexity associated with grounding a measurement circuit can beuseful, for example, for reducing complexity of a medical procedure.

In certain implementations, a thermocouple 251 can be disposed along theirrigation element 128. For example, the thermocouple 251 can bedisposed on one or both of an outer surface or an inner surface of theirrigation element 128. The thermocouple 251 can be in electricalcommunication with, for example, the processing unit 109 a. In use, theprocessing unit 109 a can adjust one or more parameters related to rateof irrigation fluid delivery through the irrigation element 128, timingof irrigation fluid delivery through the irrigation element 128, or acombination thereof, based on a signal received from the thermocouple251. Additionally, or alternatively, the processing unit 109 a can alertthe physician if the signal received from the thermocouple 251 isinconsistent with an expected irrigation rate.

Electrical activity detected (e.g., passively detected) by the centerelectrode 235 and the sensors 226 (acting as surface electrodes) canform the basis of respective electrograms associated with each uniquepairing of the center electrode 235 and the sensors 226. For example, inimplementations in which there are six sensors 226, the center electrode235 can form six electrode pairs with the sensors 226 which, in turn,form the basis for six respective electrograms.

An electrogram formed by electrical signals received from eachrespective electrode pair (i.e., the center electrode 235 and arespective one of the sensors 226) can be generated through any ofvarious different methods. In general, an electrogram associated with arespective electrode pair can be based on a difference between thesignals from the electrodes in the pair and, thus more specifically, canbe based on a difference between an electrical signal received from thecenter electrode 235 and an electrical signal received from a respectiveone of the sensors 226. Such an electrogram can be filtered or otherwisefurther processed to reduce noise and/or to emphasize cardiac electricalactivity, for example.

Because the center electrode 235 remains spaced at an intermediatedistance from the sensors 226 and tissue in the range of forcesexperienced through contact between tissue and the deformable portion242 of the ablation electrode 224, the electrogram formed from eachelectrode pair can advantageously be a near-unipolar electrogram. Asused herein, a near-unipolar electrogram includes an electrogram formedbased on the difference between two electrodes that are greater thanabout 2 mm apart and less than about 6 mm apart and oriented such thatone of the electrodes remains spaced away from tissue. In certainimplementations, in the absence of force applied to the deformableportion 242 of the ablation electrode 224, the center electrode 235 isspaced apart from the sensors 226 by distance greater than about 2 mmand less than about 6 mm.

The near-unipolar electrograms associated with the center electrode 235spaced from the sensors 226 can provide certain advantages over unipolarconfigurations (i.e., configurations having electrode spacing greaterthan 6 mm) and over bipolar configurations (i.e., configurations havingelectrode spacing equal to or less than 2.5 mm and/or allowing bothelectrodes to be spaced close to tissue). For example, as compared tounipolar electrograms, the near-unipolar electrograms formed based onsignals received from the center electrode 235 and the sensors 226 areless noisy and, additionally or alternatively, less susceptible tofar-field interference from electrical activity away from the tissue ofinterest. Also, as compared to unipolar electrograms, a near-unipolarelectrogram does not require a reference electrode on a separatecatheter or other device. As a further or alternative example, ascompared to bipolar electrograms, a near-unipolar electrogram formedbased on signals received from the center electrode 235 and the sensors226 is generated from an electrode pair with only one electrode in theelectrode pair in contact with tissue such that the resultingelectrogram waveform arises from one tissue site, making it less complexto interpret. Also, or instead, as compared to bipolar electrogramsgenerated from a pair of electrodes in contact with tissue, the signalof a near-unipolar electrogram formed based on signals received from thecenter electrode 235 and the sensor 226 in contact with tissue can havea more consistent morphology and/or a larger amplitude at least becausethe center electrode 235 is always oriented away from tissue as comparedto the sensor 226 in the electrode pair touching tissue.

The sensors 226 can be any of the various different sensors describedherein and, in addition or in the alternative, can be arranged on thedeformable portion 242 of the ablation electrode 224 according to any ofthe various different arrangements described here. For example, in theabsence of external force applied to the deformable portion 242 of theablation electrode 224 enveloping the center electrode 235, the sensors226 can be noncoplanar relative to one another. It should be appreciatedthat, as compared to a planar arrangement, the electrograms generatedfrom the sensors 226 arranged in such a noncoplanar configuration can beuseful for providing improved directional information regardingelectrical activity in tissue.

The sensors 226 can be electrically isolated from the deformable portion242 of the ablation electrode 224 with the sensors 226, acting assurface electrodes, passively detecting electrical activity in tissue inproximity to each respective sensor 226 without interference from thedeformable portion 242 of the ablation electrode 224. At least some ofthe sensors 226 can be at least partially disposed along an outerportion of the deformable portion 242 of the ablation electrode 224 withthe deformable portion 242 of the ablation electrode between the centerelectrode 235 and at least a portion of each respective one of thesensors 226 along the outer portion. Additionally, or alternatively, atleast some of the sensors 226 can be at least partially disposed alongan inner portion of the deformable portion 242 of the ablation electrode224. In such implementations, each sensor 226 can be in proximity totissue without touching tissue as the deformable portion 242 of theablation electrode 224 touches tissue. Thus, for example, at least someof the sensors 226 can extend through the ablation electrode 224.

Referring now to FIGS. 1 and 22-23, the catheter 204 can replace thecatheter 104 in FIG. 1. Accordingly, electrical signals from the sensors226 and the center electrode 235 can be directed to the catheterinterface unit 108 and, thus, unless otherwise indicated or made clearfrom the context, should be understood to form a basis for detectingcontact with tissue, detecting deformation of the ablation electrode224, or a combination thereof, according to any one or more of themethods described herein. For example, the signals can be sent to anelectrical input stage associated with the catheter interface unit 108.In certain implementations, the difference between electrical signals isdetermined through electronic circuitry (e.g., a voltage amplifier witha differential input). Additionally, or alternatively, the differencebetween electrical signals can be determined by the processing unit 109a of the catheter interface unit 108.

In general, the storage medium 109 b of the catheter interface unit 108can have stored thereon computer-executable instructions for causing theprocessing unit 109 a to acquire a plurality of electrograms (e.g., anelectrogram for each electrode pair formed by the center electrode 235and each respective sensor 226). The storage medium 109 b be can, alsoor instead, have stored thereon instructions for causing the processingunit 109 a to display a representation of at least one of the pluralityof electrograms on the graphical user interface 110. In certainimplementations, the storage medium 109 b can have stored thereoninstructions for causing the processing unit 109 a to determine avoltage map associated with the plurality of electrograms, the voltagemap corresponding, for example, to electrical activity of a heart of apatient. In some implementations, the storage medium 109 b can havestored thereon instructions for causing the processing unit 109 a todisplay the voltage map on the graphical user interface 110. Thedisplayed electrograms, alone or in combination with a displayed voltagemap, can be useful for selectively treating tissue of the heart (e.g.,delivering ablation energy from the deformable portion 242 of theablation electrode 224 to tissue in a cavity of the heart).

Referring now to FIG. 24, the irrigation element 228 (FIG. 23) can beformed from a substantially planar sheet of material rolled into a tube233 (e.g., a substantially cylindrical tube). It should be appreciatedthat various features of the irrigation element 228 can be formed in thesubstantially flat sheet prior to or while the substantially flat sheetis formed into the tube 233. More specifically, material can be removedfrom the substantially planar sheet of material (e.g., through lasercutting) to form leaflets 236, the plurality of irrigation holes 234, ora combination thereof. As compared to forming features on a curvedmaterial, it should be appreciated that forming the leaflets 236, theplurality of irrigation holes 234, or a combination thereof on thesubstantially planar sheet can reduce manufacturing complexity and, alsoor instead, facilitate controlling spacing and size tolerancesassociated with the plurality of irrigation holes 234 which, in turn,can facilitate controlling a spray pattern of irrigation fluid throughthe plurality of irrigation holes 234.

Once the tube 233 is formed, the nozzle portion 229 of the irrigationelement 228 (FIG. 23) can be formed by, for example, bending theleaflets 236 toward each other to form a substantially closed end of theirrigation element 228. In certain implementations, the bent leaflets236 can be joined to one another (e.g., through welding) at seamsbetween the leaflets 236 adjacent to one another.

Referring now to FIGS. 21, 22, and 25, one or more of the sensors 226can be supported on the deformable portion 242 of the ablation electrode224 through an orifice 237 defined at an intersection of struts 244 b(e.g., at a joint). For example, the sensor 226 can extend from anexterior surface of the deformable portion 242 to an interior surface ofthe deformable portion 242. Arranged in this way, the sensor 226 cancome into contact with tissue along the exterior surface of thedeformable portion 242 and, additionally or alternatively, the portionof the sensor 226 extending to the interior surface of the deformableportion 242 can be connected to wires carrying electrical signals asnecessary for using the sensor 226 to measure contact with tissue,measure electrical activity of tissue (e.g., electrograms), orcombinations thereof.

In certain implementations, the sensor 226 can be formed as a rivetsecurable to the deformable portion 242 through the orifice 237. Agrommet 239 can be disposed in the orifice 237, between the sensor 226and the deformable portion 242 of the ablation electrode 224. Thegrommet 239 can be formed, for example, of an electrically insulatingmaterial (e.g., any of various different biocompatible polymers) spacedbetween the sensor 226 and the deformable portion 242 of the ablationelectrode 224. In this way, the grommet 239 can electrically isolate thesensor 226 from the deformable portion 242 of the ablation electrode224. Additionally, or alternatively, the grommet 226 can be formed of apliable material to facilitate, for example, press fitting the grommet239 and the sensor 226 through the orifice 237.

In general, the grommet 239 can reduce the likelihood that mounting thesensor 226 in the orifice 237 will interfere with operation of thesensor 226. For example, the grommet 239 can facilitate mounting thesensor 226 to the deformable portion 242 of the ablation electrode 224without requiring physical modification (e.g., drilling) of the sensor226.

Referring now to FIG. 26, current density through the deformable portion242 of the ablation electrode 224 (FIG. 21) in the uncompressed statewas simulated using a finite difference method. In the simulation, theablation electrode 224 was assumed to have uniform voltage (e.g., 1 V),with the medium set at uniform resistivity. The return electrode wasassumed to be the edge of the domain and was set to another uniformvoltage (e.g., 0 V). It is believed that the variation in simulatedcurrent density along a trajectory (shown as the arc extending fromposition 0 to position 450) at a fixed distance away from an outersurface of the deformable portion 242 is a proxy for the actualvariation in current density along the respective trajectory of thedeformable portion 242.

Referring now to FIGS. 26 and 27, the simulated current density throughthe deformable portion 242 varies by less than about ±10 percent alongthe trajectory at 1 mm away from an outer surface of the deformableportion 242 in the uncompressed state. Thus, the current density at afixed distance near the deformable portion 242 in the uncompressed stateis believed to be relatively uniform. Thus, more generally, currentdensity near the surface of the deformable portion 242 is substantiallyinsensitive to the orientation of the deformable portion 242 relative totissue. Further, given that the deformable portion 242 in the expandedstate is larger than a maximum lateral dimension of the catheter shaft222 (FIG. 21), the deformable portion 242 can reliably deliver widelesions in any of various different orientations relative to tissue.This can be useful, for example, for reducing treatment time and/orincreasing the likelihood that applied ablation energy is sufficient totreat a targeted arrhythmia.

While the results shown in FIG. 27 are based on a simulation using afinite difference method, the general observations drawn from thesesimulations are supported by the experimental results described below.

FIG. 28 is a graph of depth of lesions applied to chicken breast meatusing the ablation electrode 224 (FIG. 21) in axial and lateralorientations relative to the chicken breast meat. Each lesion wasperformed on chicken breast meat and 0.45% saline solution at bodytemperature and, for each lesion, the deformable portion 242 of theablation electrode 224 (FIG. 21) was in contact with the chicken breastmeat with 10 g of force and 8 mL/min of irrigation was used. For eachablation, 2 amperes were delivered to the tissue through the deformableportion 242 (FIG. 21) for ten seconds. Lesion depth was determined usinga ruler to measure the depth of tissue discolored from pink to white.

Five of the lesions were created with the deformable portion 242 (FIG.21) in an axial orientation in which the catheter shaft 222 (FIG. 21)was perpendicular to the chicken breast, and five of the lesions werecreated with the deformable portion 242 in a lateral orientationperpendicular to the axial orientation. As shown in FIG. 28, althoughthe lesions were created using different orientations, the lesion depthswere similar, with lesion depth varying by less than about ±20 percent,indicating that the amount of energy ablating tissue in bothorientations is similar. This experimental finding is consistent withthe results of the simulation. That is, lesions corresponding tomultiple different angles between the deformable portion 242 (FIG. 21)and tissue have similar depth at each of the multiple different angles.Such uniform distribution of current density can facilitate controllinglesion size, which can be particularly useful for ablating thin tissue.

While a center electrode has been described as being disposed on theirrigation element, it should be appreciated that a center electrode canadditionally or alternatively be located at any of various differentpositions within a deformable portion of an ablation electrode. Forexample, a center electrode (e.g., the center electrode 235 in FIG. 21)can be positioned on a distal end portion of a catheter shaft.Additionally, or alternatively, an irrigation element (such as theirrigation element 228 in FIG. 21) itself can be used as a centerelectrode. Thus, for example, the irrigation element can be at leastpartially formed of an electrically conductive material and used as areference electrode, a driven/grounding electrode, or a combinationthereof.

While ablation electrodes have been shown and described as includingcertain substantially spherical deformable portions, it should begenerally understood that a substantially spherical deformable portion,as described herein, can include a deformable portion, in anuncompressed state, having at least a hemisphere (e.g., at least adistal hemisphere) lying within a range of the larger of about ±1 mm orabout ±25% of a nominal radius from a center point. Thus, for example,referring now to FIG. 29, an ablation electrode 324 can have adeformable portion 342 having a distal region 344 and a proximal region346. Unless otherwise indicated or made clear from the context, theablation electrode 324 should be understood to be useable instead of orin addition to any one or more of the ablation electrodes describedherein. Thus, by way of example and not limitation, the ablationelectrode 324 should be understood to be useable in place of one or moreof the ablation electrode 124 (FIG. 2), the ablation electrode 124′(FIG. 18), the ablation electrode 124″ (FIG. 19), and the ablationelectrode 224 (FIG. 21), unless otherwise indicated or made clear fromthe context.

In general, the deformable portion 342 can be substantially spherical inan uncompressed state. That is, in the uncompressed state, the distalregion 344 of the deformable portion 342 can be at least a hemispherelying within a range of the larger of about ±1 mm or about ±25% of anominal radius “R” from a center point “P”. In FIG. 29, for the sake ofclarity, the hemispherical extent of the deformable portion 342 is shownin only two dimensions. Given the three-dimensional extent of thedeformable portion 342, however, it should be appreciated that therelationship shown in FIG. 29 applies in three dimensions.

In certain implementations, the proximal region 346 of the deformableportion 342 can be shaped differently from the distal region 344 in theuncompressed state. For example, the proximal region 346 can besubstantially conical in the uncompressed state. As used herein, asubstantially conical shape of the proximal region 346 should beunderstood to include any one or more of various different shapes forwhich, in the uncompressed state, the shortest distance from each pointalong the proximal region 346 is less than about ±1 mm from a frustum ofa right circular cone 348. For example, the frustum of the rightcircular cone 348 can have a radius of a first base of about 1 mm orgreater and a radius of a second base of about 6 mm or less, with theradius of the first base less than the radius of the second base.

In general, it should be appreciated that the ablation electrode 324having a substantially spherical shape including a substantially conicalproximal region 346 can have any one or more of the advantages describedherein with respect to other ablation electrodes and, thus, should beunderstood to offer advantages with respect to one or more of uniformcurrent density near the outer surface of the ablation electrode 324 andrepeatable positioning of struts, cells, and/or sensors as thedeformable portion 342 moves from a compressed state to an uncompressedstate. Further, or instead, as compared to other shapes, the ablationelectrode 324 having a substantially spherical shape can be lesstraumatic to tissue (e.g., when there is contact between the deformableportion 342 and tissue of the heart). Additionally, or alternatively, ininstances in which a maximum radial dimension of the ablation electrode324 is larger than a maximum radial dimension of a distal portion of acatheter shaft, the formation of the proximal region 346 assubstantially conical can facilitate proximal movement of the ablationelectrode 324. That is, continuing with this example, the substantiallyconical shape of the proximal region 346 can be, as compared to othershapes, less resistant to proximal movement into or within, for example,the heart, the vasculature, a sheath, an insertion sleeve, or anycombination thereof.

While ablation electrodes have been described as including deformableportions, other configurations of the ablation electrode areadditionally or alternatively possible. For example, the ablationelectrode can include a plurality of struts (e.g., any of the strutsdescribed herein) defining a plurality of cells, with the struts forminga substantially rigid structure that maintains a shape in response toforce exerted on the ablation electrode. For example, the plurality ofstruts can form, for example, a substantially rigid structure having amaximum radial dimension substantially equal to a maximum radialdimension of a catheter shaft to which the substantially rigid structureis coupled (e.g., directly or indirectly coupled). In use, one or moreof irrigation fluid and blood can flow through the cells of thesubstantially rigid structure as described with respect to any one ormore of the ablation electrodes described herein. Additionally, oralternatively, any one or more of the surface electrodes describedherein can be carried on the substantially rigid structure, and thesubstantially rigid structure can envelop any one or more of the centerelectrodes described herein. Thus, by way of example, one or moresurface electrodes carried on the substantially rigid structure cancooperate with a center electrode enveloped by the substantially rigidstructure such that that contact with tissue of an anatomic structure isdetected.

The above systems, devices, methods, processes, and the like may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. This includes realization inone or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors or otherprogrammable devices or processing circuitry, along with internal and/orexternal memory. This may also, or instead, include one or moreapplication specific integrated circuits, programmable gate arrays,programmable array logic components, or any other device or devices thatmay be configured to process electronic signals.

It will further be appreciated that a realization of the processes ordevices described above may include computer-executable code createdusing a structured programming language such as C, an object orientedprogramming language such as C++, or any other high-level or low levelprogramming language (including assembly languages, hardware descriptionlanguages, and database programming languages and technologies) that maybe stored, compiled or interpreted to run on one of the above devices,as well as heterogeneous combinations of processors, processorarchitectures, or combinations of different hardware and software. Inanother aspect, the methods may be embodied in systems that perform thesteps thereof, and may be distributed across devices in a number ofways. At the same time, processing may be distributed across devicessuch as the various systems described above, or all of the functionalitymay be integrated into a dedicated, standalone device or other hardware.In another aspect, means for performing the steps associated with theprocesses described above may include any of the hardware and/orsoftware described above. All such permutations and combinations areintended to fall within the scope of the present disclosure.

Embodiments disclosed herein may include computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps thereof. The code may be stored in a non-transitory fashion ina computer memory, which may be a memory from which the program executes(such as random access memory associated with a processor), or a storagedevice such as a disk drive, flash memory or any other optical,electromagnetic, magnetic, infrared or other device or combination ofdevices.

In another aspect, any of the systems and methods described above may beembodied in any suitable transmission or propagation medium carryingcomputer-executable code and/or any inputs or outputs from same.

The method steps of the implementations described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So, for example performing the step of X includes anysuitable method for causing another party such as a remote user, aremote processing resource (e.g., a server or cloud computer) or amachine to perform the step of X. Similarly, performing steps X, Y and Zmay include any method of directing or controlling any combination ofsuch other individuals or resources to perform steps X, Y and Z toobtain the benefit of such steps. Thus, method steps of theimplementations described herein are intended to include any suitablemethod of causing one or more other parties or entities to perform thesteps, consistent with the patentability of the following claims, unlessa different meaning is expressly provided or otherwise clear from thecontext. Such parties or entities need not be under the direction orcontrol of any other party or entity, and need not be located within aparticular jurisdiction.

It should further be appreciated that the methods above are provided byway of example. Absent an explicit indication to the contrary, thedisclosed steps may be modified, supplemented, omitted, and/orre-ordered without departing from the scope of this disclosure.

It will be appreciated that the methods and systems described above areset forth by way of example and not of limitation. Numerous variations,additions, omissions, and other modifications will be apparent to one ofordinary skill in the art. In addition, the order or presentation ofmethod steps in the description and drawings above is not intended torequire this order of performing the recited steps unless a particularorder is expressly required or otherwise clear from the context. Thus,while particular embodiments have been shown and described, it will beapparent to those skilled in the art that various changes andmodifications in form and details may be made therein without departingfrom the spirit and scope of this disclosure and are intended to form apart of the invention as defined by the following claims, which are tobe interpreted in the broadest sense allowable by law.

1. A catheter comprising: a catheter shaft having a proximal end portionand a distal end portion; an irrigation element positioned relative tothe catheter shaft to direct irrigation fluid distal to the distal endportion of the catheter shaft; and an ablation electrode coupled to thedistal end portion of the catheter shaft, the ablation electrodeenveloping the irrigation element, and the ablation electrode includingstruts coupled to one another at joints to define collectively aplurality of cells, wherein each cell of the plurality of cells isbounded and the coupled struts are movable relative to one another suchthat a maximum radial dimension of the ablation electrode increases byat least a factor of two as the coupled struts move relative to oneanother to transition the ablation electrode from a compressed state, inthe presence of external force, to an uncompressed state, in the absenceof external force.
 2. The catheter of claim 1, wherein the struts are inelectrical communication with one another to form a single electricalconductor.
 3. The catheter of claim 1, wherein the ablation electrodeincludes an inner portion and an outer portion, opposite the innerportion, and the inner portion is in fluid communication with the outerportion through the plurality of cells.
 4. The catheter of claim 1,wherein, in the uncompressed state, at least some of the struts extendcircumferentially with respect to an axis defined by the proximal endportion and the distal end portion of the catheter shaft.
 5. Thecatheter of claim 1, wherein the catheter shaft defines a center axisextending from the proximal end portion to the distal end portion, andat least some of the cells of the plurality of cells have a respectivesymmetry plane passing through the respective cell and containing thecenter axis of the catheter shaft.
 6. The catheter of claim 1, whereinthe catheter shaft defines a center axis extending from the proximal endportion to the distal end portion, and at least some of the cells of theplurality of cells have a respective symmetry plane passing through adistal end of the cell, a proximal end of the cell, and the center axis.7. The catheter of claim 1, wherein at least some of the cells of theplurality of cells have a larger area in the uncompressed state of theablation electrode than in the compressed state of the ablationelectrode.
 8. The catheter of claim 1, wherein, in the compressed state,strain in the ablation electrode is less than about ten percent.
 9. Thecatheter of claim 1, wherein at least some of the plurality of cells aresubstantially diamond-shaped in the uncompressed state.
 10. The catheterof claim 1, wherein the struts are formed of nitinol.
 11. The catheterof claim 1, wherein a combined area of the plurality of cells along anouter surface of the ablation electrode is greater than a combinedsurface area of the struts along the outer surface of the ablationelectrode.
 12. A catheter comprising: a catheter shaft having a proximalend portion and a distal end portion; an irrigation element positionedrelative to the catheter shaft to direct irrigation fluid distal to thedistal end portion of the catheter shaft; and an ablation electrodeincluding a distal region and a proximal region, the proximal regioncoupled to the distal end portion of the catheter shaft, and the distalregion including struts coupled to one another to define collectively aplurality of cells, wherein each cell is bounded by at least four of thestruts, and the struts are coupled to one another to define a closedshape along the distal region, the closed shape of the distal end regionenveloping the irrigation element.
 13. The catheter of claim 12, furthercomprising a fastener coupling the struts to one another to define aclosed shape along the distal end region.
 14. The catheter of claim 13,wherein a portion of the struts define respective eyelets through whichthe fastener extends to couple the portion of the struts to one another.15. The catheter of claim 14, wherein the eyelets are aligned with oneanother.
 16. The catheter of claim 14, wherein the fastener is a rivet.17. The catheter of claim 14, wherein the fastener extends through theeyelets at a distalmost position of the ablation electrode.
 18. Thecatheter of claim 14, wherein the plurality of cells includes a firstset of cells and a second set of cells, the first set of cells arebounded by the portion of the struts defining respective eyelets, thesecond set of cells are bounded by the struts without eyelets, and thesecond set of cells are bounded by fewer struts than the first set ofcells.
 19. The catheter of any one of claim 12, wherein the struts areformed of nitinol.
 20. A method of forming a catheter, the methodcomprising: forming an ablation electrode having two open ends, theablation electrode including struts collectively defining a first set ofcells, a portion of the struts having a first end region coupled toanother one of the struts and a second end region uncoupled from each ofthe other struts; inserting a fastener through the respective second endregions of the portion of the struts to couple the second end regions toone another to define a second set of cells and to close one of the twoopen ends of the ablation electrode; and coupling the ablation electrodeto a distal end portion of a catheter shaft.
 21. The method of claim 20,wherein, with the second end regions of the portion of the strutscoupled to one another, the ablation electrode is resiliently flexiblebetween a compressed state, in the presence of an external force, and anuncompressed state, in the absence of an external force.
 22. The methodof claim 20, wherein the second end region of each respective strut ofthe portion of struts defines an eyelet and inserting the fastenerthrough the respective second end regions of the portion of strutsincludes aligning the eyelets of the second end regions such that thefastener is inserted through the aligned eyelets.
 23. The method ofclaim 20, wherein forming the ablation electrode includes removingmaterial from a tube of material to form the first set of cells.